In my experience, boys tend to be more assertive on what they want. If they have a question, they tend to do it right there and then. Girls on the other hand might not be as assertive. If they have a question they might be embarrassed to say it in front of people. This is not always the case though. There are a lot of girls who are very assertive and there are many boys who are shy. That is why I think boys tend to ask more questions in class and girls ask more questions by email.