The proportions achieving A* to B were similarly above national averages, whilst those achieving the top grades were in line, with 27% of all entries grades A* or A.
The overall was pass rate was 99%.
Cllr Susan Chappell, Richmond Council Cabinet Member for Schools, said:
“This is a fantastic set of results. This is only the third year since our secondary schools opened their sixth forms, giving parents and children greater local choices.
“Over 400 students selected their school sixth form as a preferred local option and 99% of them passed! Plus, with 85% getting A* to C – our sixth forms are already performing way above the national average. Seeing improvements since 2016 is particularly impressive given the changes to the A-Levels.
“My congratulations go to the pupils, teaching staff and governors for their achievements and the amazing work that they do.”