There are very strict rules in place about exclusion.
the school is exepected to take a whole raft of steps first, eg internal exclusion etc.
Expulsion cannot come out fo the blue, there has to be evidence of breaking behaviour code, then consequence and so on until the final consequence of expullsion.
At each stage where other children are involved the school will be doign a ris assessment to safeguard the other children.
Eg a child who is violent and puts other childrne at risk may need to be accompanied at all times, especially outdoors at playtimes.
The school is in some ways between a rock and a hard place, because they have to consider the welfare of both the victim and the perpetrator, givne that both are children and the perpetrator may be in very vulnerable circumstances.
if a child is excluded, that may throw them back into a situation which is veyr bad for them, as there is no-where else for them to go.
Not easy for the school. But in the end it has to prioritise the safety of all children in its care.