Jo MacKinnon, assistant head of Parrs Wood high, Manchester, said the A2 was much harder. "We have actually been advising some students not to take chemistry, for example, to full A-level, even if they have done well at AS."
Richard Kemp, head of Pate's grammar school in Cheltenham, said: "Students have found it extremely tough." He said the number doing four A-levels had halved as a result.
Maths was a particular problem. Julia Jama, head of sixth form at Whalley Range high, Manchester, said: "The maths syllabus is extremely dense and challenging. Half our maths AS students decided not to take it to the full A-level."
But many schools and colleges welcomed the flexibility of the new system. Ann West, of Lewisham College, said: "At a college like ours, it is particularly important that students have something to show for their efforts after one year.
"Many young people have found the jump from AS to A2 huge and may want to leave education and go into employment at the AS stage."