Children have been told they will be banned from cycling to their south London school if they do not put number plates on their bikes.
Teachers at Stanley Park High, in Carshalton, are introducing the scheme so members of the public can report pupils cycling dangerously.
The secondary school said the main aim was to keep children safe.
Charity Cycling UK questioned why Stanley Park High "want to make cycling to school more difficult".
On the school's website, head teacher Amit Amin wrote: "All students who cycle to school will be required to display a school-issued bicycle number plate when riding to and from school.
"Students without a number plate will not be permitted to cycle to school, or lock their bicycles on school grounds."
Mr Amin said the measure was in response to incidents of children cycling in a way that "endangers themselves and others".
'Trespassing' on parental duties
A school statement added: "Our absolute priority is the safety of our students, and the aim of this initiative is simply to ensure their safety as they travel to and from school."
The plates are being introduced on 1 October as part of a scheme to encourage cycling, which includes subsidised bike lights and maintenance workshops.
Duncan Dollimore, of Cycling UK, said Mr Amin's actions were "part of a trend of head teachers trespassing on parental responsibilities".
Mr Dollimore said schools should focus on encouraging local authorities to adopt 20mph speed limits and traffic-calming measures instead of making "cycling to school more difficult".
If I was one of the school governors, I’d be stepping in about now... https://t.co/YTLJzXMJfL— Chris Boardman (@Chris_Boardman) September 24, 2018
Another critic of Stanley Park High's policy is Chris Boardman, former professional cyclist and Greater Manchester's cycling and walking commissioner.
He wrote on Twitter: "If I was one of the school governors, I'd be stepping in about now."