Our first Headmaster, Neil Harcourt MacNeil was a Military Cross recipient and a Rhodes Scholar. Under his leadership, the School grew rapidly in size and academic achievement. He set the tone for Knox as a school that educates the whole boy, which is still evident today. He led the School from 1924 to 1939 and went on to become the Headmaster of Wesley College until his death in 1946.

The School was officially opened by Sir George Fuller, Premier of NSW, on the afternoon of 5 February 1924. Classes commenced the next day with 28 boys, six of whom were Boarders. The youngest boy was aged eight and the oldest 13. 'Earlston' had been purchased in 1923 to house the School and was aptly named 'School House'. This building was both the residence of the Boarders and the Headmaster, and where classes were held.

The Main School Building was the School's first purpose-built facility providing classrooms, assembly rooms and laboratories, as well as the Headmaster's Office. The building was designed by Power, Adam and Munning Architects and built by H K MacKenzie. It was opened by Duncan Carson, President of the Highland Society, on 12 February 1925 and extended in 1927.

In the School’s first Annual Report it was noted that it was the students who planted the grass on the Oval. The Headmaster calculated that by the end of the first year they had planted "the equivalent of a furrow reaching from the School to Sydney Town Hall". By Winter Term 1925, Rugby was being played on Knox 1 for the first time.

'Innisfail' was purchased from the Armstrong family in 1928 and renamed 'Ewan House'. It became the home of the Knox Preparatory School from 1929. The old drawing room became an assembly hall and the music room became a common room. The Billiard room was split into the Boarders' locker room and a classroom. The Prep School was known as Ewan House for many years.

The pool and gymnasium were made possible by a generous donation of £100 by R N Briley, a Schoolmaster from 1925 to 1927. The Parent's Association took up the idea and by the end of June 1928, the School had been promised £1,500. Howie Moffatt & Co. estimated that it would cost £2,500. The pool and gym officially opened on 9 November 1929. The Reid Industrial Arts Building now stands on the site of the original swimming pool.

In 1929, soon after commencement of the year, Headmaster MacNeil announced that Prefects would join Seniors and Probationers as school leaders. He appointed four, one for each House and the School Captain. M R Arnott (OKG29) Captain of the School, G L Kenway (OKG29), T G McKinney (OKG30) and S M FitzSimons (OKG28) were the first School Prefects. Marcus Latham (the Schoolmaster from 1927 to 1933), is credited with introducing the House and Prefect system of the English public schools to Knox.

The founding meeting for the Old Knox Grammarians' Association (OKGA) took place on April 1929 at the YMCA Sydney and 13 Old Boys attended. The first OKGA Committee was formed under the leadership of chairman Justice R Le Gay Brereton (OKG28), Hon. Treasurer N Sky (OKG28) , and Hon. Secretary R Morson (OKG29) and the Committee was made up of W Perry (OKG28) and N Rhodes (OKG28). The chief objective of the OKGA was to keep Old Boys connected with the School and each other. In 1930, the OKGA's first constitution was approved.

The May 1929, the Knox Grammarian described the School's first drama production as follows: "The Importance of Being Earnest was far in excess of expectations. Outstanding in the cast were W P Ash (OKG31), J S Yeomans (OKG33), and C S Peebles (OKG29). G L Kenway (OKG29) was excellent as Rev Chasuble. The proceeds from the drama production were used to purchases a set of hurdles to be used for Track and Field."

The Knox Grammar School Cadet Unit dates back to 1924 when Headmaster MacNeil formed the School’s Drill platoons. In the 1927 Knox Grammar School Annual Report, Mr MacNeil noted that Drill platoons produced ‘grand virtue and steadiness’ and from then, on the Headmaster’s direction, all students were required to Drill as a company and each School House was represented by a platoon.

Since 1924, Knox attended the combined annual service at St Stephen's Presbyterian Church in Phillip St, Sydney city. In 1931, Knox held its very own Anzac Day service for the first time where the Reverend James, a former minister of Wahroonga, addressed the School on the meaning of Anzac. After the service, the School marched past the Colours.

Our first memorial gate, The Fitzhardinge Gate, was erected in 1933 in remembrance of Brian F H Fitzhardinge (OKG33), a pupil at Knox Grammar School from 1925 to 1931, and who died in 1932. His mother donated the iron gateway as a nod to her sons and many other boys who crossed through the campus from the south as a shortcut to the Main School Building.

In 1937, military authority was received to form a military band in lieu of one platoon. The School promptly ordered six extra bugles and eight drums. The Military Band practiced Mondays and Wednesdays with junior members taking an additional practice on Fridays. The Military Band was the precursor to the Brass Band and the Pipe Band, which were formed in 1946.

For the comfort of the boys, Headmaster Dr William Bryden (1939-1953) suggested a summer uniform of khaki shorts and an open necked shirt, strictly to be worn only in the school grounds. It was not until February 1941 that the final step was taken and the boys appeared in the summer khaki uniform still worn today. The Knox tie is now worn with the summer uniform. The uniform was also used as the summer Military Drill uniform.

In 1939, Muriel, the Scottish wife of Headmaster Bryden, suggested the formation of a pipe band. In 1946, a tutor was teaching nine boys on four sets of bagpipes. The Pipe Band played in the 1948 Anzac Day parade with drummers borrowed from the Brass Band. In 1950, the band began wearing the MacPherson Tartan, which was chosen as the families of Mrs Bryden, John Adamson (Council Chair 1945-1952, Council 1939-1952) and the Gillespie family had links to the clan.

In August 1950, six teachers and 23 students embarked on a 20-day scientific expedition to Central Australia. They arrived in Adelaide by plane and embarked on a train journey to Finke Railway Siding, 160 miles from Alice Springs. They transferred to Blitz Wagons to travel to Uluru. The cost for each boy was 53 pounds. Boys were split into six groups: Anthropology, Geology, Photography, Biology, Geography and Navigation and Communications.

The Knox Parents and Friends Association (KPA) was formed at the end of 1954 as an initiative by Headmaster Dr Couper. Justice Le Gay Brereton was elected as the first President at the inaugural meeting chaired by Mr George Sinclair (Council Chairman 1952-1955, Council 1944-1969). Early KPA projects raised funds for the needs of the School, including a filtration plant for the swimming pool and construction of the Memorial Quadrangle. Today, every parent is considered a member of the KPA and encouraged to take part in its many activities including Knox Gala Day, Knox at Home and the Knox Christmas Markets.

Prime Minister R G Menzies opened the Old Boys’ War Memorial on Anzac Day, 1955. The Roll of Honour featured 47 names and was read by the School Captain. A Ceremonial Parade followed on the oval, a pattern that has been followed now for seven decades. The OKGA pledged funds to the construction of the Memorial Gates, a Roll of Honour and a sandstone wall facing the Pacific Highway. The Quadrangle and Memorial Gates were designed by Joseland & Gilling Architects. The preliminary plans were drawn up by Gordon King (OKG35), brother of Desmond, whose name appears on the memorial.

The first Garden Day was held on 25 September 1957 as an initiative of the Knox Upper School Mothers Group. Three gardens were opened to the public for inspection and a guest speaker spoke about the gardens and plants. Stalls sold plant cuttings and served morning and afternoon tea. In 2016, the event was changed to a Spring Festival and was last held in 2017.

In 1960, the widow of one of William McIlrath – one of the original benefactors from St John’s Presbyterian church in Wahroonga, Catherine, McIlrath offered the School £50,000 pounds to build a chapel in memory of the School’s Old Boys killed in WWII. The Knox Grammar School War Memorial Chapel, designed by J Aubrey Kerr and built by J G Post, was opened on 4 November 1962 by Lieutenant Governor Sir John Northcott. The Chapel contained one stained glass window designed and installed by artist David Saunders of Eroica Studios, the East Window. It was the gift of Dr and Mrs Winston-Smith (daughter of Mr William McIlrath School Council member 1923–1955); it depicts the life, death and resurrection of Christ.

Early in the 1965 Rugby season, the 15A team took a tour to the North Island of New Zealand. This was, according to the Knox Grammarian, the first time a Knox team had travelled outside Australia. The tour, organised by W Lawson (Sportsmaster 1959-1994), was declared a benefit to the 20 players who took part.

The Knox Class of 1967 was the first to sit the Higher School Certificate (HSC) with 92 of the 190 students electing to participate. As a result, 25 students received a Commonwealth University Scholarship, four students received a Commonwealth Advanced Education Scholarship (for tertiary study other than university) and nine students received Teacher’s College Scholarships.

Knox Grammar School’s first musical, Oliver, was performed in 1973. The orchestra consisted of just ten boys. Abbotsleigh and Pymble Ladies’ College students joined the chorus and played the female leads. The performance was an outstanding success. Oliver was performed again as a whole School production at the opening of the Junior Academy and Performing Arts Centre (JAPAC) in 2019.

In 1974, the School celebrated its 50th year in style with a Thanksgiving Church Service, an OKGA Jubilee Ball, an Art Exhibition, Dinners in Newcastle, Armidale and Melbourne, OKG vs School Football matches, a Dinner Dance, an OKGA Dinner and a Cocktail Party. The Jubilee Year also saw the opening of two significant buildings, the Prep Oval Building and the Senior School Library Building (McKenzie Building since 1984). To mark the occasion, the School also produced a Jubilee Album, of the music of Knox, featuring the Pipe and Brass Band.

In 1977, a uniquely Australian church was formed, the Uniting Church in Australia. This church was established through the union of three Christian denominations – the Methodist, Congregational and Presbyterian churches. At the time of union, most Presbyterian congregations and schools chose to join with the new church. It was at this time that Knox Grammar became a Uniting Church School, as did St John’s Uniting Church in Wahroonga.

On Saturday 2 April 1977, the inaugural Gala Day was held to open the Football season. It was attended by a large number of parents and students to watch the House Rugby competition, Soccer competition and browse the market stalls. Three teams from each House competed in seven-a-side games. MacNeil House came out on top at the end of the day, winning both Rugby and Soccer senior competitions. Barbecue lunches and an array of stalls supplied everything from books to fruit and vegetables were provided by the Knox Parents' Association.

From 1924, students wore a dark grey suit, however a sports blazer was introduced by Headmaster MacNeil (it resembled one he wore as part of his Oxford University Rowing team). The sports blazer was worn over the sports uniform before and after matches and first appears in team photographs from 1929. The School Council began phasing in the blue woollen 'dress' blazer as a standard uniform for all students. The 1986 School Prefects photograph is the first to show all students wearing the new blazer. The Heritage Centre is fortunate to hold the blazer of Academy Award nominee and Knox Grammar 1986 School Captain Hugh Jackman AC (OKG86). The heavy woollen blazer was eventually replaced by a lighter, more functional and comfortable material.

The Senior Knoxonians is a group of Old Boys distinguished by having completed their schooling 50 years ago or more. Initially called the Over 70's Club when established in 1984, prominent among the members were Norman Winter (OKG31), Jim Bartlett (OKG31), Ian Ferguson (OKG32), Mac FitzSimons (OKG28) and Geoff Crapp (OKG30). Its constitution stated that members were to be at least 70 years of age and the aim of the Club was to meet regularly to renew and strengthen the bonds of friendship made at school. Early meetings were held at members' homes until numbers grew too large and it subsequently moved to the School function spaces. The first President was Jim Bartlett, who held the position for seven years until 1990. Norman Winter was the Secretary/Treasurer in 1992. The Club later changed its name to The Senior Knoxonians.

The first Knox student recipient of the Rhodes Scholarship was The Hon. Justice Ian Jackman (OKG80). The Rhodes Scholarship is a fully-funded, full-time, postgraduate award which enables talented young people from around the world to study at the University of Oxford. Knox has had five graduates receive this prestigious award. The most recent recipient was Michael Jones (OKG04) in 2011.

In 1993 the OKGA, in conjunction with the School, held the first OKGA Honouring Service. This small and moving event was held in front of the OKGA War Memorial. The next-of-kin of Old Boys who had lost their lives in service of their country, presented Ceremonial Swords and Drums to officers of the Cadet Unit.

The Sanctuary was a gift of Edith Keirle, daughter of George Gillespie, and her family. It was the demolition of the Gillespie family’s church, St Margaret’s Turramurra, that was the impetus for this project. The stained glass windows of St Margaret’s were dedicated to the Gillespies and so were offered to the School to preserve. The windows are in the traditional style and in contrast to those designed for the Chapel by David Saunders. The Font in the Sanctuary was the gift of the Class of 1939. It is dedicated to their 11 classmates who lost their lives in WWII.

In 2002, the School introduced an additional program to complement the educational opportunities offered. The da Vinci program was designed to excite, challenge and enrich academically able boys. The program encourages an approach to thinking and learning which embraces the seven principles of da Vinci learning. da Vinci included a Year 5 Preparation Program as well as programs for Years 6-8 and Years 9-12. The first da Vinci Decathlon was also held in 2002. The Academic Inter-school Gala Day hosted 32 teams with 256 students in its inaugural year.

On 17 April 2004, the new K-2 centre was unveiled and 130 Kindergarten, Years 1 and 2 boys eagerly entered their new learning space. 2004 marked the first year Kindergarten was offered at Knox Preparatory School. The first Kindergarten was made up of 40 students in two classes. In their first year, students visited Taronga Zoo, achieved 1st in Prep Track and Field and participated in the Infants Choir.

Knox held its inaugural Knox Tattoo under lights on Knox 1 Oval in 2005. Knox 1 was transformed into a specially designed, 3,000-seat arena with the added attraction of a 30sqm electronic screen. Some 250 members of pipe and brass bands from ten school and community groups were involved, along with 40 student highland dancers. The Tattoo was led by the Knox Grammar Pipe Band and was supported by Knox's Cadet Unit. The finale of the Tattoo featured fireworks and more than 1,000 members of bands, dance groups and Cadets on the parade ground at the one time.

The Knox Academy of Performing Arts (KAPA) was an initiative of Headmaster John Weeks to combine the talents of the Music and Drama Departments.

In 2008, the Knox Indigenous Program was launched by Ms Helen Clarke to support and assist Aboriginal and Torres Strait Islander students to navigate school life and share their cultural journey. The Indigenous students are empowered to engage with and share their culture through cultural mentoring, Yarning Circles, Acknowledging Country at large gatherings, smoking ceremonies and dancing. The program connects the School with local cultural Elders, peoples and organisations to provide opportunities for all students to learn about the First Nations histories, cultures and peoples.

The Knox Boarding Centre was opened in 2010 as a purpose-built space for Boarding students and staff. Featuring modern accommodation for 135 Boarders ranging from Years 7-12, the Centre houses an ensuite for every two boys, individual desks, and storage areas; accommodation for Housemasters and Assistant Housemasters, a commercial laundry and separate kitchenettes. The Jessie Gillespie Clinic is located on Level 1 providing 24-hour access for Boarders. The Boarders' Terrace was opened in 2021 and provides the Boarding students with their own area for outdoor recreation and socialising.

The Great Hall opened in 2011 and has capacity for 2,500 people. It is a multi-purpose hall and is used for Basketball training and matches, music and theatre productions, assemblies, functions, and exams. The Hall is often used by surrounding schools for their celebrations and has hosted the Lifeline Book Sale for many years. This building project included the Aquatic Centre, home of our indoor Olympic-sized swimming pool and a Learn to Swim pool for younger children.

Knox is a founding member of Positive Education Schools Association (PESA). The Association aims to work together with schools from across Australia, New Zealand and Asia that are considered to be key 'pioneers' in the implementation of Positive Psychology.

By 2012, the Cadet Unit had expanded to seven companies including Support and Headquarter Company. The introduction of Cadets from Ravenswood School for Girls only enriched the experience of the Cadets from both schools. By 2013, the girls were fully integrated throughout all companies and the numbers grew to more than 1,000 Cadets with a fifth recruit company needing to be added. In 2021, a student from Ravenswood led the Knox Ravenswood Cadet Unit for the first time, Senior CUO Emma Woodcock.

The Knox Total Fitness Action Model represents the holistic academic, social and emotional, spiritual, and physical wellbeing of each individual in our School community. This model seeks to ensure our evidence-based approach to wellbeing and positive education is embedded and spread across inter-connected school systems. Every student has an individual mentor who has received expert training in Wellbeing Science and Positive Psychology. The mentor helps students to identify their strengths and set academic and personal goals. All Knox staff receive gold standard training in key aspects of Positive Psychology and Wellbeing Science.

The Senior Academy, for Years 11 and 12 students, is an example of Headmaster John Weeks’ fondness for "innovation wrapped in tradition". While the facade is in the traditional Scottish Baronial style, the interior presents a flexible learning environment: a Senior’s Hall for teaching, study, and socialising; senior library, technology-rich classrooms with moveable walls, dedicated Legal and Business Studies classrooms including a corporate-style boardroom; a 150-seat lecture theatre, a café, and an outdoor recreation area. The Knox Senior Secondary Academy was named the Weeks Senior Academy in 2018 to honour the contribution of John Weeks and his wife, Denise.

Established in 1926, Wahroonga Preparatory School (WPS) is a co-educational campus for girls and boys from Pre-Kindergarten to Year 6. In 2016, Knox Grammar School acquired WPS adding more than 200 students to the School's community. WPS uses the St John’s Uniting church, the church hall, and original church manse as part of their campus facilities thus reconnecting the School to its original benefactors and founders. The WPS students were invited to join the Knox Gallery Choir, held special events at the Senior School campus and undertook Learn to Swim lessons in the Aquatic Centre.

Scott James was appointed Headmaster in April 2018. A highly-educated and passionate leader, Mr James completed a Bachelor of Arts and Graduate Diploma in Education at the University of Technology and a Master of Educational Leadership at the University of Wollongong. He is a member of the Australian College of Educators, the Australian Institute of Company Directors, the Australian Council for Educational Leaders (ACEL) and is a Board Member of Positive Education Schools Australia. He has also completed a school leadership program at Harvard Graduate School of Education. Mr James has more than 25 years’ experience as an educator. He has led the implementation of Knox’s Positive Education program, Knox Total Fitness, and is passionate about using mental fitness and a growth mindset to empower young people. In 2018, Mr James and the School Council made the decision to add Courage to the School's core values of Faith, Wisdom, Integrity and Compassion. The Headmaster stated that a school cannot approach prominence or inter-generational sustainability without the risk-taking and courageous actions of its leaders.

Originally known as KG1, the Academy of Global Competency is dedicated to students in the Middle Academy, Years 9 and 10. It provides a flexible and open plan learning environment for individual and group work. The facility is technology-enabled for video conferencing and includes a canteen and recreation areas. A large meeting room is available on both levels. In 2022, the meeting room on the upper level was named The Bryden Room to recognise the contribution of our second Headmaster Dr William Bryden (1939-1954). The Thistle Room was the long-term home of Pipes and Drums named in recognition of Mrs Bryden who suggested the School create a Pipe Band.

The Performing Arts Centre was designed to inspire and promote excellence in music, dance and drama. It includes purpose specific classrooms, a 165-seat performance space, a dance and recording studio, and the Wenkart Theatre. The Wenkart Theatre is beautifully designed for an immersive theatre experience with tiered seating for an audience of 750, a large stage, an adjustable orchestra pit and cutting-edge lighting and sound equipment. The name of the theatre recognises the generous contribution of the Wenkart family to the School. Dr Thomas Wenkart (OKG61) attended the School from 1951 to 1961. His three sons David (OKG92), Scott (OKG94) and William (OKG97) also attended the School.

The Tartan Army officially began in 2020 as an initiative run by the Year 12 student leaders to bring all students from different ages, interests and backgrounds together to support Knox boys to achieve their goals in sporting and co-curricular areas. The Tartan Army inspires camaraderie and highlights traditions of war cries and community support.

The governance model of Knox Grammar School had not changed since 1924. In 2020, incorporation for all Uniting Church Schools in NSW was proposed as the schools needed structure which permitted the management of appropriate liability, perpetual succession, ownership and control over property, the ability to enter contracts in its own right, and to benefit from the oversight of Australian Securities and Investments Commission, and the Australian Charities and Not-for-profits Commission. After incorporation in 2021, Knox remains a proud Uniting Church School and continues to share the Church’s mission mission in a Relationship Agreement with with up to two Church Ministers appointed to the School Council.

In 2022, a Cadet Drill Team was reformed including 30 Cadets (15 Ravenswood and 15 Knox). The team was introduced in recognition of the first School Drill teams which formed the basis of the Knox Cadet Unit. In 2023, the Cadet Drill Team travelled to Scotland and Belgium, with Pipes and Drums, on its first overseas tour. They gained experience performing on a world stage and participated in a wreath-laying ceremony at the Menin Gate in Ypres on the Western Front.

In 2023, the Prep School House system was expanded to include three new Houses; Miles, Thomson and Armstrong, which were named after prominent figures in the School's history. Mr Richard Miles OAM (OKG39) attended Knox from 1930 to 1938 and contributed to the School in many ways. He organised for the profiles of the Class of 1939 to be gathered and published, his family foundation provides scholarships for students in need and he was also involved in the Knox Honouring Service. In 2019, he was awarded Life Membership of the OKGA, for services over many years and was the first recipient of the OKGA Thistle Medal. He received his OAM in 2015 for service to the community, particularly through roles with educational organisations. James Richard Thomson (OKG31) was the School’s first enrolled student in 1924. He was a member of the OKGA, the Senior Knoxonians and the Past Parents' Association and remained a loyal supporter of the School throughout his life. Twelve Thomson family members have attended the School and further family members are enrolled. Mrs Florence Armstrong sold her property Ewan House to the School at a reduced cost for the formation of a separate campus for Knox Prep students.