For the purpose of your course you need to teach across two consecutive age ranges. This is usually KS3 and 4 but for some subjects such as social sciences where there is often no KS3 course it may be KS4 to 5. It may be useful for you to gain some A level experience if you teach in a school that has a Sixth form but due to the high stakes exams for the students this would need to be in negotiation with the Head of the Department.