MONMOUTH School received an outstanding Estyn report on Friday after an inspection in March.
It was told performance and prospects for improvement are excellent.
The independent boarding school, on Almshouse Street, was founded in 1614 by William Jones, a member of the Haberdashers’ Company of London, and it is a part of the Haberdashers’ Monmouth school family. Its last inspection before the one in March was in 2007.
Inspectors found the school’s range of extra-curricular activities, with high pupil participation rates, contributes to pupils’ social and personal development.
The school’s headmaster, Dr Steven Connors, said: “We were delighted with the Estyn report.
“It does make very good reading and to see what we do confirmed as ‘excellent’ by an external audit is probably the best kind of reward for all the hard work. It was marvellous to receive such an outstanding endorsement in the same year we celebrate our 400th anniversary.”