I'm far from being a millennial but to allow a child to spend half the day with only one shoe and to then allow them to walk home that way is completely out of order. The school needs to be brought to account for allowing and accepting the bullying behaviour.
Bullying is and will always be prevalent in society if they persistently ignore it.
You may disagree with the philosophy of dealing with a bully and you think the behaviour is due to other traumatic events .. but it has to be crushed hard and fast with little or no pity.
You are quite right the school is totally accountable.