Girls have campaigned to wear the same uniform as boys in the past, but one school has decided to ban skirts - making trousers the only option.
The ban at Broadstone Middle School in Poole, Dorset, will be introduced in January after governors decided skirts were not suitable for some lessons.
The headteacher said the ban was "to give girls the same opportunities as boys" and to "maintain their modesty".
But some parents suspect that the ban is to stop girls wearing short skirts.
"I know some of the girls go to the school with very short skirts, but why do the majority now have to suffer as a consequence?," one parent told the local newspaper.