Angry parents say their children will be forced to wait an hour for a bus home from school due to timetable changes.
They say if the bus used by their children to get home from Prince Henry's Grammar School at Otley is cancelled, they would be stuck in the town centre after school each day.
But First Bradford, which runs the 653 Harrogate-Otley-Shipley-Bradford bus, says the changes have been introduced to improve punctuality and that alternative services are available.
Until now, the weekday 653 has picked up from Otley bus station at 4.05pm. But from today the hourly service will not arrive until 4.23pm. Prince Henry's shuts at 3.30pm.
Pauline Benson's daughter Laura, 14, is a pupil at Prince Henry's and uses the 653, changing at Shipley to get a second bus home to Thackley.
Mrs Benson, whose 11-year-old daughter Sarah is due to start at the school in September, said she was starting a petition calling for the changes to be scrapped.
She said: "Asking children as young as 11 to wait 53 minutes at the bus station just isn't on.
"It's their safety we're concerned for, especially during the winter, when it's darker - we don't want them hanging round for that length of time.
"It'll be very cold for them in the winter and if this bus doesn't come the next won't arrive until almost two hours after school's finished.
"I just can't see how putting it back 18 minutes will improve reliability - they don't seem to have thought about the children at all.''
Prince Henry's head teacher John Steel said: "I've written to the bus company backing the parents' request for them to reconsider.
"Having youngsters standing around in the town centre unsupervised isn't the best situation from a safety point of view.''
A First Bradford spokesman said the timetable change had been introduced to improve reliability on the route by giving the bus a longer gap between the completion of its previous journey and the start of the next.
He said passengers could alternatively take the First Leeds 731 or 732 services, which leave Otley at 3.40pm and 4.05pm respectively, changing at Guiseley White Cross to meet the 755 or 647 service running to Shipley.
He added: "We're reviewing the network on an on-going basis and anyone not satisfied with the timetable should get in touch. In our opinion this adjustment will make the service more reliable.''
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