1."Boys and girls both learn better in single-sex school." - While this might be true, not having daily interactions with the opposite sex might be a negative aspect later in life.
2. "Schools should let children wear whatever they want at school" - decency must be imposed. While I don't agree with compulsory school uniforms, I can't say that students should be able to wear everything.
3. "Schools don´t teach children the important things they need to know to be an adult." - that's true but I don't think it's their job to do that, they must teach you how to get a job and earn an income.
4. "School summer holidays should be shorter." - I don't think this should be the case. but it really depends on where you're living. Studying when the temperature is close to 38 C is not easy.
5. "Children spend too much time at school on maths and IT, and not enough on things like music, art, and drama." - I strongly disagree with this one. In a world that's becoming more and more dependent on technology we still have very few people who understand how it works, the vast majority only knows how to use it. And the importance of technology in our everyday life will increase so if anything else we should invest more in math and IT.
6. "Private schools are usually better than state school." - it depends. In my country state schools are better while private schools only exist to extract large amounts of money from those who want to have a diploma.