Revealing mistake: When the notice of impending strike is posted in the town, the American spelling of "labor" is used. A Welsh signwriter would have spelt it "labour."
Continuity mistake: After Huw has been beaten by his teacher and has staggered home, his brothers find him lying in the street. They are angered and horrified by what has happened - one of them says "He cut you to the bone". Yet when they pick him up to carry him home, we get a clear view of his back, and there isn't a mark on him.