I was kicked out of my secondary school's sixth form (after GCSE results)... not because I did badly, but because I was their top student and they thought I was "too bright" so they un-enrolled me without my consultation- what a nightmare that was! The school I ended up at for sixth form, despite being one of the best performers in Kent, doesn't really kick people out after bad AS results, even if they got 5 Us (yes, we were made to do 5 AS levels). If the student really wants to stay, then they're given the option of resitting the year and they can even completely change their subjects- but they can only do this once.