At William Farr school in Lincoln students are out of lessons for up to 46 weeks in the course of their seven-year secondary careers. The school year is 38 weeks.
Lessons in the summer term are abandoned for GCSE revision classes which run from the end of the Easter term. They are followed by six weeks of exams after which pupils are away until September.
Pupils taking AS or A2 are out of class for seven weeks because of the exam timetable and students who also sit modules in January have another three weeks of revision and a week of exams.
Added to this are the weeks of preparation and non-teaching time in Years 7, 8 and 9 thanks to cognitive ability tests, optional tests and statutory national tests.
The Government is facing growing criticism over a testing regime in which the average child sits 105 tests and exams between the ages of four and 18. Ministers insist testing is necessary to gauge pupil progress and demonstrate a school's effectiveness.
But Paul Strong, headteacher of William Farr, said: "Pupils are out of lessons for an incredible length of time. Or they are in class revising what they have already learned rather than learning anything new or anything in more depth."
The school's PE department loses the use of the gym for three months every year because it is commandeered as an exam hall. Sixth-formers struggle to find time to do anything other than academic work.
Mr Strong said: "Children are not enjoying Year 12. The young enterprise scheme fell apart this year, our senior orchestra is suffering and three or four talented drama students had to turn down the school play because they just didn't have the time.
"What makes it worse is admission tutors think the AS is unproven and are still going on A-level results so pupils are going through all this for nothing."
Year 7: cognitive ability tests - one week Year 7: end of term and progress tests - one week Year 8: end of term and optional tests - one week Year 9: national curriculum tests - two weeks for revision, one week for tests Year 10: end of term tests - one week Year 11: week of mocks, three weeks' study leave in May, six weeks of exams and off for the remaining three weeks Year 12: January AS modules - three weeks' revision and week of exams Year 12: seven weeks of summer AS exams Year 13: December mock A2 exams - one week Year 13: January A2 or AS resits - three weeks' revision and a week of exams Year 13: seven weeks off in the summer for A2-examsresits. Off for the remaining three weeks of term Total: 46 weeks.