Gosh, what an awful situation but one sadly far more common than you think. Retired TA here and what works within a school is a paper trail so emails subject headed " safeguarding BoB Davies ( obviously his own name ) and never give up. I'd explain that situation in writing to the school and copy in one of the school governor's.
Not only did I see a lot of this which then creates a meeting etc, I have had social workers / us TA'sand Senc and head if year etc attend these meetings and a team of professionals then is aware and pieces of the puzzle begin to be observed if that makes sense and sometimes the pupil is lucky enough for a professional to fit the pieces together with the right knowledge.
Pre Warning re Tonight’s Eastenders