Abel, Your Brother (1970)

Karol is a newcomer to the class and instantly called "sissy". He makes himself disliked by correcting his classmates and eating sandwiches, while everybody else eats dry bread and onions. He tries to make friends with class bully called Balon, and eventually succeeds. The group uses him to steal lollipops and later for an assault on a small child. The victim's mother seeks out the responsible and Karol is identified. He eventually confesses to his mother and names his accomplices. Branded now as a "squealer" he is avoided by his former friends. During a concert Karol collapses and is carried off.