The school was opened in September 1966 on its former Llanedeyrn Road, Cyncoed site as an 11-16 school and provides a church school comprehensive education for secondary students living mainly in the eastern half of Cardiff. It is now one of three Voluntary AidedSecondary Schools in the Diocese of Llandaff and serves a much wider geographical and spiritual 'catchment' area; many students come from the Diocese of Monmouth and as far away as Caerphilly. As a Voluntary Aided school, the Local Education Authority maintains it, but the Church through its Governing Body, has considerable spiritual, financial, administrative, and educational duties towards it. The teaching staff are appointed by the Governing Body and have a responsibility to ensure that the curriculum and general life of the school is maintained through a sound Christian foundation. The school moved to a new building located on the former playing fields of Llanedeyrn High School in September 2013, after Llanedeyrn High School closed. Today, the school accommodates around 1400 Christian, faith and non-faith pupils between the ages of 11 and 18, with year groups 7 to 11 and an optional sixth form. In 2015 the school created controversy when they demanded that pupils provide a doctor's note to be allowed to use the lavatory during lesson periods. This system is still in place and enforced by staff to reduce the number of students taking breaks during lessons, especially where their intention is to avoid the lesson. In June 2019, it was announced that headteacher Ceri Weatherall would step down from her post, and that current deputy headteacher Ian Loynd would take up the role from September 2019.
New building
In September 2013, St Teilo's High School officially moved from its location on Llanedeyrn Road to the playing fields of Llanedeyrn High School, with the former site becoming the home of Ysgol Gyfun Gymraeg Bro Edern. The new school was designed by architects in a 'five finger' design, to accommodate over 1400 pupils. The school has a curved design which acts as a sound barrier against the noise pollution caused by the large volume of traffic on the nearby A48 road. However, air pollution is an issue due to the school's close proximity to the A48. The school has 97 full-size classrooms, of which 8 are ICT computing suites. As part of the new building, a biometric payment system was introduced. Students can now pay for lunch using their fingerprint and load money onto their account via ParentPay, as well as being able to print using their biometrics through PCounter Secure Printing. A deal was also reached with the local Sony UK Technology Centre in Pencoed to provide digital signage services, projectors and video recording facilities for the school. The school was built in 5 stages, the last stages including the construction of the MUGA, 3G pitch and football and rugby playing fields.
Uniform
The school uniform has changed multiple times over the decades, with navy blue polo shirts used up until July 2016. In September 2016, St Teilo's reverted its uniform design back to traditional blazers following their surge in popularity with nearby schools, as well as their current use in sixth form. As with the previous uniform, years 7 to 9 have a different set of uniform to years 10 and 11, who also have a different set of uniform to sixth form. Instead of polo shirts, students now have to wear white shirts and themed ties with the option of either a blazer or jumper. The school's black shoes rule has remained from the previous uniform policy. Sixth form students wear a maroon colour jumper or a sixth-form branded blazer instead of the navy blue colour scheme used by the lower years.
