Schools never exclude without good reason.
If only that were true. I have sat on appeal panels: the vast majority of exclusions were upheld, but there was still an ongoing number of cases where schools excluded for essentially petty reasons, or after completely failing to investigate properly.
I remember one where the children concerned were smoking in an area outside the school: the headteacher excluded them permanently for smoking cannabis, but there was absolutely no evidence that they were - she didn't have the cigarettes they were smoking, she didn't take hand swabs (which schools have the power to do), and when challenged about it she just said that that was what she believed. And another where there was a whole horror story about a child throwing a two-litre bottle of water at the front window of an underground train and bringing the underground system to a halt with a security scare - only, when asked, the train company concerned knew nothing whatsoever about it and CCTV showed that all the kid had done was to kick a pebble onto the line.
And then there was the one where a very dyslexic child of 13 had the same totally inadequate statement he had had at age of 7: no-one had thought to reassess his needs when he became disruptive at age 10, or when he had a managed move from his secondary school as he was on the brink of exclusion, and he was excluded from the second school in his second term there. The school seemed astonished at the idea that maybe his behaviour might be a product of unaddressed dyslexia, or indeed that behavioural problems themselves might constitute a learning difficulty which they had a duty to deal with.
Bear in mind that, for all these cases, the appeal panel included a headteacher who was very robust and if anything biased towards the school, but in each case the headteacher concerned was shocked at the decision the school had taken.
And don't get me started on the schools (most frequently academy and church schools) that have a big upturn in exclusions in Year 11 which just happen to be exclusions of the children most likely to make a dent in their GCSE stats ...