The claimant complained about a dress code which said men must dress in a "professional and businesslike way", with a collar and tie. Women had to "dress appropriately to a similar standard" but continued to wear T-shirts.
The tribunal said it was discriminatory for men to be required to wear particular clothing while women were not.
But the appeal concluded that this was the wrong approach. The tribunal should have asked whether men and women could only achieve equivalent smartness if men wore a collar and tie.
Further challenges to dress codes look set to be made, following the new regulations outlawing discrimination by sexual orientation and religion.
But schools which still believe in particular dress standards should not be deterred. They can impose a dress code on staff that is different for men and women. The trick is to ensure that the overall effect does not lead to less favourable treatment for one sex.