Tacal a home/school book can help, IF school use it correctly and know what it is being used for ie to help monitor behaviours and identify triggers for the behaviour, which will be helpful so both you and school are noticing them and decide where support is/isnt needed.
All it managed to achieve in ds's old school, was school thinking I was being critical and blaming them. For example I would write that ds had been self harming and had sores and he appeared confused about x,y,z. School would just get defensive and write that he wasn't confused and was fine!! I would then ask which methods they have used to establish that he wasn't confused and was fine and they would ignore my question!! So totally pointless!
I think firstly you need a school who are at least willing to acknowledge that children can present differently at home/school. Secondly that children can be very anxious in school, but not show outward signs in school.
'Fine' to some schools equals he is not screaming or throwing chairs, so therefore not a problem to them.
and a big NO, small schools are not always better, the worse MS school ds went to was small, one class per year. EXPERIENCE and EXPERTISE and above all else a willingness to UNDERSTAND, COMMUNICATE and WORK WITH PARENTS is what makes a school better.
There is no trumps when you have a kid with SN's, im sure its just as upsetting and worrying for you, as it is for me
Ds never stops self harming (apart from if he doesn't have to attend school at all), it started when he was 5 and started school. We have times when self harming is reduced or increased, its how ds communicates his feelings. His self harming wont improve unless school deal with the underlying issues, his inability to express his feelings verbally, his social communication, interaction and how confusing he finds it.
Im hoping I have found a willingness to understand in his new school. If you have already tried with this school and tried again and they are just unwilling to work with you, then try another school