I would say that this was probably your mistake. Your work history is on your application form and yet they still interviewed you. Don't make a big deal out of it in interviews. There should be no gaps at all., think of something that you were doing to fill in the spaces. If you leave gaps they will probably assume you were in prison or the like. Also realise that there is no shortage of teachers and that NQTs are cheaper than someone far at the payscale. It is possible that you are doing nothing fundamentally wrong, just there are too many teachers for too few jobs.