Key Stage 3 (KS3) is the legal term for the three years of schooling in maintained schools in England and Wales normally known as Year 7, Year 8 and Year 9, when pupils are aged between 11 and 14.

Key Stage 4 (KS4) is the legal term for the two years of school education which incorporate GCSEs, and other exams, in maintained schools in England, Wales and Northern Ireland—normally known as Year 10 and 11 in England and Wales, and Year 11 and Year 12 in Northern Ireland, when pupils are aged between 14 and 16.