I agree with your points, Wa11esey, and good points from the other posters too.
Even a sma11 action, like a warning or a word in the ear from the person in charge (teacher, head, playground supervisor), would send a clear signal what behaviour is acceptable or unacceptable in school.
Mi55 Snowdrops has just turned 11 and is sti11 in Juniors.
She might be a child who shrugs things off or
a sensitive shy one..but having your hair pu11ed nearly to the ground whether in Juniors or secondary is absolutely not an enjoyable thing to endure.
That is not how a person should behave if things do not go their way i e tantrums, rudene55,physical attacks.
I think the Head is rightly appa11ed that that went on.
As for when is the right time to step in...
I suppose the punishment should fit the crime.
if it's a sma11 incident, a word of warning to chastise the behaviour.
if a persistent offender, bring out the stocks!!... or whatever schools sanctions are these days.