The attitude of your parents isn't the major influence, though. In a society that pushes for gender roles, while you can still try as a parent to not enforce them, this won't help much.

When you look at studies (and there are many which analyse the disparities in school) they often conclude it is because basically teachers like the girls more since they are more often quiet and tidy. Sadly, many studies who used anonymised tests still had handwritten tests or don't mention whether they were handwritten, which I think is a huge oversight.

Also, boys are globally less likely to spend time on their homework, which was directly linked to worse grades. Here is an interesting bigger study: OECD study Underperformance in Boys

Interestingly, even with better grades, people still overall believe girls are good in school because they are diligent and boys are good because they are intelligent. I wonder if that couldn't also influence the way some teachers give marks. The stereotype that girls lack talent