Dozens of pupils were sent home on the first day of term after their uniform did not comply with school rules.
In all around 90 children from Ysgol Rhosnesni were sent home yesterday, a decision that has angered parents.
Andy Brant, the new headteacher at Ysgol Rhosnesni, said the school had made it clear they "would be respectful, yet uncompromising" when enforcing the dress code in this new academic year.
In a statement, Mr Brant said: "In July, I wrote to all parents on two occasions clarifying expectations for uniform.
Ysgol Rhosnesni students Lydia Jones, Lily Arrowsmith, Chloe Lynch and Rily Douglas with their parents
"Colleagues and I were pleased to see that the vast majority of our students arrived today [Wednesday] looking exemplary.
"However, a number of students arrived wearing trainers or inappropriate skirts.
"In my previous communications with parents, I made it absolutely clear that we would be respectful, yet uncompromising when enforcing our dress code in the new academic year, and before the summer holiday many parents contacted me to express their support for a more rigorous and consistent approach to standards at Ysgol Rhosnesni.
"I am genuinely committed to making Rhosnesni the best school in North Wales and this will not happen without consistently high expectations for all students.
"It is encouraging that this ambitious vision is fully supported by the School Governing Body and the majority of parents and students."
Debbie Lynch was one of the parents whose child was sent home, in her daughter's case for inappropriate footwear.
She said: "There's no need to send children home for something like this.
"I would understand if it was kids wearing brightly coloured trainers or clearly wrong uniform, but it's not. They're being sent home for things like wearing black trainers or wearing white socks or having skirts that are too stretchy.
"Our children are missing out on education because of these pointless rules on uniforms. Wearing trainers doesn't effect children's ability to learn.
"It's making a mockery of their learning and I think it's pathetic.
"Schools are quick to take parents to court if they don't send their children to school, but nothing happens if the schools send the children home.
"There are loads of parents who feel the same way and I know that I will be sending my kids to school in the same stuff again."
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