When I was a lad!
Anyone who was 16 before the end of the Xmas term could leave at Easter, these people did not sit any exams. The rest of us had to be 16 by 1st September. However I distinctly remember by my School stating the officially leaving date as 25th June 1982, however, I was not 16 until July so if I wanted to be pedantic I could say left school at 15. Of course 20 years of every Secretary of Education feeling obliged to "improve" the education system things may have changed.