Governors at Diss High School in Norfolk have agreed that a trouser-only uniform will be adopted from September, based on the recommendations of a uniform focus group.
"Girls already wear trousers at Diss High School. The reason the school is making this compulsory is the tendency for some girls to wear really short skirts," Jan Hunt, school's head teacher, was quoted as saying by the Norfolk Eastern Daily Press.
"Hemlines have risen to a level that is both impractical as well as immodest," he said.
"Inevitably, this decision is popular with some parents and not with others. The same responses would be true for pupils. Financial support will be offered to parents to support this transition," he added.
The decision to introduce the ban was recommended by the uniform focus group, consisting of governors, pupils and staff, which met during the autumn term, the report said.
The review group's recommendations were then discussed by a meeting of governors, which agreed to the ban along with a number of other proposals, including a ban on make-up for children in years 7-11 and permission to wear black ballet-type shoes.
A spokesman for Norfolk County Council was quoted as saying: "In terms of uniform policy that is not something we administer, it is purely down to the school to make that decision."