adding to fat_ninja's points, you can also say school uniforms cancels out the need to waste an hour of time taken to decide what to wear to school
Just don't think of points for your side, think also about the opposition's points, so that you can counter them
They might say
school uniforms take away the freedom of the students
or
school uniforms do not make us look "COOL" or "HOT"
think of as many counter points as you can. You can say that school is not a place to be cool or hot, its a place where you learn. If they say the uniforms are not comfortable, you tell them that the uniforms will be made comfortable through a school president or someone with that authority,
BEST OF LUCK.