Parents have been told their children will be excluded if they miss detention to attend a doctor’s appointment.

Highbury Grove School wrote to parents saying they will not be able to reschedule after-school punishments - even if it means missing appointments or leaving younger siblings stranded.

The rule applies to any pupil guilty of “persistently or significantly” disrupting learning, for which he or she will be given a same-day “C3 level” detention of up to 90 minutes.

One parent labelled the school “heartless” and “extreme”, but others are said to be pleased by its “serious” approach to pupil behaviour.

Headteacher Tom Sherrington said in a letter to parents that the rule was a way of “tightening” the school’s new behavioural system, introduced in October. The detentions, issued after two warnings, previously allowed parents to reschedule in the case of medical appointments.

He told the Gazette: “There’s a small group of students who will seek every opportunity to get their way out of detention. This is very time-consuming for everyone and waters the system down.

“The way we see it, they are old enough to take responsibility. So if they disrupt lessons knowing they have an obligation after school, they should deal with that.”

The consequence of missing a “C3” detention is a one-day exclusion from school.

One parent, who didn’t wish to be named, said: “It really is quite heartless, and extreme. I can’t imagine any employer being able to do that.

“They have crossed the line: denying rights to family, or health.

“Then, if someone does miss the detention, they face exclusion – possibly for making an ethical decision in picking up a sibling.”

But Cllr Caroline Russell, whose Highbury East ward covers the school, said other parents were in support. “This is a school that has worked really hard to turn itself around for many years,” she said.

“The tone of the letter is very tough, but speaking to parents, there’s a context of pupils who haven’t been taking it very seriously.

“What the school is attempting to do is probably for the best of everybody’s education. It has worked very hard. Ten to 15 years ago, we would be almost be talking about riots on Highbury Fields. There was a lot of bad behaviour.”

Islington Council’s education boss Cllr Joe Caluori said: “We strongly support good discipline in our schools, which is essential for young people to get the most from their education.

“Individual arrangements are a matter for schools.”