A: You know what the feedback said: is it similar to what was given at other recent interviews? If not, put it down to experience. However, you are a maths teacher and I would expect you to find a new job fairly easily.
Assuming you are going for jobs at an appropriate level, then you need to ask someone who knows you well what might be the problem. It doesn't have to be a head of department; a colleague will do, if they can be honest about your teaching skills.
You are clearly conscientious, as your sample lesson plan demonstrates, and you thought through what you wanted to achieve plus the rationale behind it. Maybe you were just unlucky, but it does come back to control, as that is the only thing that I have to go on in your question. If your work spans a wide range of different age and ability groups and you can cope with them successfully, then it must be something else. If, however, your present timetable doesn't contain much work with low ability teenagers, then perhaps this is the area that potential employers are concerned about. Maybe a first impression is getting between your ability and an interview panel's perception of you.
John Howson is a recruitment analyst and visiting professor of education at Oxford Brookes University. To ask him a question, email him at firstname.lastname@example.org.