The Trinity School of John Whitgift, usually referred to as Trinity School, is a independent boys' day school with a co-educational sixth form, located in Shirley Park, Croydon. Part of the Whitgift Foundation, it was established in 1882 as Whitgift Middle School and was a direct grant grammar school from 1945 until 1968, when it left the scheme. The present name was adopted in 1954, to avoid confusion with Whitgift School. The school's head is now a member of the Headmasters' and Headmistresses' Conference (HMC).

The school's first home was in Church Road, central Croydon, and then from 1931 to 1965 it was at North End, Croydon, in the old premises of Whitgift School, which moved to Haling Park, South Croydon. The "romantic Gothic towers and verdant lawns" at North End, a building of historical significance, dominated the area, but in 1968 the whole edifice was torn down for redevelopment, despite public opposition. Today, the Whitgift Centre stands on the site, in a modernist contrast to the old building.

The school was built in 1965 on the site of the former Shirley Park Hotel.

The school is part of the Whitgift Foundation, alongside Whitgift School and the Old Palace School for Girls. The Whitgift Foundation was founded in 1596 by John Whitgift, Archbishop of Canterbury. His legacy allows the School to provide facilities and a range of bursaries and scholarships.

Trinity School was founded in 1882 as Whitgift Middle School. Its original site was in Church Road in central Croydon, occupying the modest buildings of the Croydon Poor School which dated from 1858. In 1931 it moved to its second site in North End in Croydon. After years of confusion with Whitgift School, in 1954 Whitgift Middle School was renamed Trinity School of John Whitgift. However the school's Old Boys' Club was still known as the Old Mid-Whitgiftians until early 2010, when a vote was taken to change the name to the Trinity Mid-Whitgiftian Association.

The school was a direct grant grammar school from 1945 until 1968, when it left the scheme but continued to take LEA-funded pupils until the late 1970s.

Trinity School moved to its present and third home in Shirley in 1965, built on the site of the Shirley Park Hotel, which itself was a redevelopment of a large Georgian house called Shirley House, built in 1720, once a home of the third Earl of Eldon.

Many of Trinity's pupils come from local schools and so join aged 10 or 11, but there is also a large intake of prep school boys at 10, 11 and 13+. A traditional curriculum is studied by all pupils, with optional subjects at GCSE such as Mandarin Chinese becoming more popular.

The school has a co-educational Sixth Form, a feature that was implemented in September 2012. For this change, a new state-of-the-art Sixth Form Centre was built, and opened by the Mayor of London, Boris Johnson.

Trinity has enjoyed regional and national success in its main school sports of rugby union, field hockey, cricket, and water polo, and also in other sports as diverse as swimming, athletics, and squash. The school has a climbing wall, two large astro-turf pitches and four hard tennis courts, along with pitches for rugby, cricket, soccer, and athletics, as well as the school's nearby field, Sandilands, and an indoor sports centre, with two large halls, several squash courts, a gymnasium, and an accompanying weights-room.

The school offers over 100 clubs and societies. The school’s music facilities include a recording suite and a dedicated choir room. Trinity became the first All Steinway School in London in 2012 and now has 25 pianos, including two model D concert grand pianos and five further grand pianos.

The Trinity School chess club has achieved great success over the years. One of its members, Laurence D. Marks, won the under-21 British championship in 1973, and its teams were in the finals of the British Schools Chess Championship in 1967, 1969, and 1972.

Trinity Boys Choir, led for many years by David Squibb, is well known for its outstanding musical achievements, especially through its choristers under the direction of Director of Music, David Swinson.

The current headmaster is Alasdair Kennedy, previously Deputy Master at Dulwich College, who joined the school in September 2016 on the retirement of Mark Bishop.

• 1882-1908: William Ingrams
• 1905-1919: Rev G A Jones
• 1919-1951: Horace Clayton
• 1952-1972: Oliver Berthoud
• 1972-1994: Robin Wilson
• 1995-1999: Barnaby Lenon
• 1999-2006: Christopher Tarrant
• 2006–2016: Mark Bishop
• 2016–Present: Alasdair Kennedy

The Combined Cadet Force (CCF) at Trinity consists of the three sections (Army, RAF and RN). Pupils have the opportunity of joining the CCF in the Spring Term of the Third Form and the minimum length of service is four terms. Cadets then follow a common recruits' syllabus for two terms before choosing which of the three sections they wish to join. At the end of the Summer Term all cadets have the option to attend a UK Central Camp.

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Former pupils of Trinity School of John Whitgift are known as Old Mid Whitgiftians.

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