I'd say that it is a chance for children to practise respect and cooperation with the opposite genders at a co-ed school. Women and men created with differences. Children should learn about those differences, how to work together instead of fighting which gender is better. Also i have seen girls from girls-only school, they either too shy or too aggressive when boys are around. Not all but i rather have my children comfortable because in real life, both genders exist and live together, right?
Cons: teenage love starts early so parents have to monitor.