Hundreds of pupils were handed detentions on their first day back at school - because they forgot to bring sharpeners or rubbers.
In one form group at Colne Valley Specialist Art College in Huddersfield, West Yorkshire, 20 out of 22 students were given detention.
By the end of the day, the number was reported to have hit 500, equating to one in three pupils at the secondary school.
Sarah Sykes, mother of 11-year-old Hannah, told her daughter to boycott the hour-long detention, dubbing the crackdown "ridiculous".
"I think they have taken it too far," she told local paper the Examiner. "Are they running a military school or a high school?"
Other punished offences included forgetting calculators, pencil sharpeners and rubbers.
"I got a detention even though I didn't have maths today," the student said.
But headteacher Carol Gormley defended the school's strict new policy, saying a letter was sent out to parents during the Easter holidays to ensure their children had the required equipment on their return to school.
"It is extremely disruptive to learning when large volumes of students need to borrow stationery. We educate our students to be responsible for their own organisation and it is unacceptable to arrive at school without basic equipment.
"It can be difficult for parents to appreciate how much this particular problem can get in the way of teaching in such a large school," Gormley added.