I've just moved my DD (year 2) to a mixed prep school. Boy/girl ratio seemed ok (about a third girls) but one girl in her class has left already so only 6 left. Other years have recently seen girls leave. What would be too few girls in a year?
DD has brothers, it's a very male dominated house. She's very comfortable with boys (a little too much at times) so I've no worries about not getting male contact as she grows up. I'm more worried that she will miss out on the female side of things (as she's naturally very girly) and only have a small friendship circle.
There is a really good local girls prep that provides lots more clubs (not just girly stuff) and she would have a bigger pool of friends to choose from. But I'd feel so bad moving her again. It is nice for her to have boys as friends but I'm feeling female friends (or lack of) will be more important as she grows up