"Dressing gowns on the schoolyard are not appropriate."
Some parents shamed others for choosing to wear dressing gowns, saying it was "embarrassing".
One disgruntled dad told local news outlet Teesside Live he was "absolutely sick of it".
"It's not hard to get dressed in the morning.
"Imagine how much those kids are going to be ridiculed when they get into school.
"They don't even put on a fresh pair to come and collect them. A lot of the parents are disgusted by it."
Another mum, Aimee Baker, echoed his thoughts on sleepwear.
"My oldest who came here is 17 now and they were doing it then. They're local parents and it takes only two minutes to chuck some clothes on so there's no reason," she said.
"It's embarrassing for the children. There's no excuse, you should get washed and dressed every morning."
Another parent said: "It's not just a dressing gown though it's full pyjamas, then a dressing gown and slippers. It's just normal around here now."
One dad worried the children at the school would start imitating their parents. But he's doubtful the new rules will change the way parents dress for pick-ups and drop-offs.
"They never listen to what the school says so I doubt it's going to change unfortunately," he continued.
Other Facebook users slammed the new dress code: "Who cares?"
"Why does everyone judge others so much? I mean I don't and wouldn't but it's cold, if they want to wear a dressing gown leave them to it," one wrote.
"They might have had a bad morning or struggling with their mental health or just want to climb back in bed when they get home. Big deal."
Another added: "I totally agree, judge judge judge that's all anyone does. At least they are getting their children to school.
"No one knows anyone's circumstances and what it took for them to be able to get out of bed and get the kids ready and to school."