Parents are up in arms after around 50 children were apparently "segregated" and sent home from school for not conforming to the dress code.
The Beacon School in Banstead, Surrey, reportedly sent the students home after they returned from half-term on Monday.
Pupils whose parents could not be reached were kept in "isolation" and not allowed to go to classes.
On its website, the school states it is "is very proud of the high standards of appearance created by our students wearing school uniform" and it "expects" students to wear the specified clothing.
"Students should avoid extremes of fashion in terms of the uniform or hairstyles."
But one parent told a local paper it was "pathetic" her 15-year-old son had been sent home from school.
"As far as I'm concerned he's not gone in with pink hair but a pair of black shoes."
Her son was sent home for wearing black plimsolls, rather than the leather-style shoes specified in the school's uniform criteria.
"What's more important, our kids' education or the material of their shoes?" she added.