Malmesbury School achieved fourth place in the tables for the number of GCSE grades A* to C but headmaster Tim Gilson said it is even better than that.
He said: “In my reckoning we are the best non-selective school in the county. The schools above us are either independent or selective so the results across the board are very pleasing.
“But Wiltshire as a whole always performs extremely well and we are all very fortunate to live in the county.
“Of course, there are always things to improve and our attainment figures at A-level are not quite as good as they were last year. On the other hand, our value-added figures are better.
"Like all other schools we concentrate on our less advantaged students, a group that historically under-achieves, and the staff have been making extra effort to bring their performance up.
“Our attendance figures are excellent due to the time taken by our staff to address that.”