The Mayville School bus was travelling along Holbrook Road, Landport, when the attack happened.
A dad of a pupil said: ‘Young lads were throwing things and a brick smashed a window.
‘All the kids got showered in glass, but luckily none of them were hurt.
‘My daughter had a little nick on her hand.
‘They were very lucky.’
The incident happened at about 4.15pm.
The damaged bus had to return to the school and police were called.
The dad added: ‘It’s not on. They are only young kids.
‘Some of them were terrified. I don’t know why they would do that.’
Anyone with information should call Hampshire police on 101.