Counter-Argument against Co-education!

I'm having trouble, coming up for a counter-argument against Co-Education!
Here is what I have so far:

Despite the average perception that single-sexed education benefits students in terms of academic achievement. Studies prove the assumption that "girl's do better in an all girls school and boys do better in an all girls," by a study that was conducted in 2005-2006 by the Strategic Counsel.

This sentence is not complete.

Also, I think you wrote this wrong: "girl's do better in an all girls school and boys do better in an (all girls???),"

Okay, studies show that test scores are higher in an all boys or all girls school, but is education's only purpose to bring about high test scores?

Here is a hint for you... google this:
Purposes of education list
functions of education list

:-)