Well, mister, i think you have some points but in general, single sex education is bullshit. I don't want to explain it too long, i will also read opinions to your 4 problems.
Boys are always getting distracted. In that kind of knowledge-based society backed with technology, you can't make them fully focused to their classes. If you mean that distraction by sexually, i should say man always wants to have things out of his grasp. So you take girls away from them, they probably skip the class and go to see the girls or be porn addicts.
Mentality difference creates brain storm which is wonderful at education. Besides, if man and woman knows mentality of each other, it would be a wonderful place to start in future discussions.
If you make children to respect each other, respect to their boundries and completely explain what decency is, they make their best to avoid from it. Explanation is the best way to keep them away from faults. Forbids are just make faults alluring.
There should be global educational mind-set apart from religions. Of course that mind set should respect religious borders but i never saw in any verse in Quran that forbids man and woman stand together. It only forbids indecency.
Conclusion is; come on! It's 21st century! We should discuss which planet going to be habited. Not single or co-education...