Question

Can anyone give me sources which have statistics where single sex schools beat coeducational?

Answer 1

You appear to be asking for data which supports a particular conclusion/assumption. Look up the term "confirmation bias".

Next look up "single sex schools research", keeping in mind that many private schools and many studies funded by private schools (both single sex and coed), may also produce data which is just as biased as your question.

However, bias can be largely mitigated by using http://scholar.google.com/ instead of the normal google.com.