How can it be fair to remove a valid choice from one person, because another feels that they cannot take that choice up it up -even when the choice is theirs to make, and entirely feasible?
How are you removing a choice from girls when they currently don't have that as an option? You aren't removing anything from girls. Their position is unchanged. They are no worse off than they are now. They have 2 options and will continue to have 2 options, whilst boys only have 1 option currently.
Fair' and 'equal' are both idealistic principles - not real things.
Ok. Give boys equality when it comes to school uniform then. Still the same principle. Equality doesn't mean the same.