YA - 90s - MC teenage boy - Roma family - girl in red skirt

From POV of teenage boy. Set in UK. He lives with half sister who is younger and has a crush on him, but he is not interested in her in the slightest. She tried to impress him by getting her bellybutton pierced but it just grosses him out.

A group of Roma (referred to as gypsies in the book) travellers arrive in their town and he falls in love with the girl who wears a long red skirt.

One of the other students helps the girl catch up with schoolwork by writing English grammar on the blackboard at lunchtime. Kids aren't allowed write on the board and the MC thinks they'll get in trouble so he flips out and wipes it all off, frightening the girl. Turns out the teacher had given permission and MC ends up looking like an arsehole. He is mortified.

People in the town are apprehensive about the Roma group at first, but come to accept them.

Some incident kicks off and the group leave. They leave all the gifts people gave them behind because they're tainted by what happened.