Unfortunately depending on what part of the country you are, it can be very difficult to find a school for all the trainees. When I started my PGCE last year a lot of students on my course didn't have a placement when the school experienced started, and many had to start 3/4 weeks later. If there are no schools available then there's not much that can be done. As the previous poster has already pointed out, new trainees are the main priority, not those who have to repeat a placement. Depending on the situation, special consideration can be given to trainees who fall slightly short of the "number of school days experience" quota.