The head at the Pindar School Mr Bellamy told Newsround's website he's trying to make sure the school is healthy, and said: "fish and chips once a week are acceptable".
Mr Bellamy explained to Newsround's website that a while ago all the children were allowed out of school at lunchtime.
But when Mr Bellamy took over he found that this was making the school unpopular with older people who can feel scared of big groups of children.
Rule change cost shops cash
Now kids have to stay in school during lunchbreak, but the shops where they were spending their cash were losing loads of money.