There's not really any plausible explanation as to why so many left-handed students tend to skew towards boys, rather than girls, other than social contagion.

There's not really any plausible explanation as to why so many left-handed students tend to skew towards boys, rather than girls, other than social contagion. When my parents were kids, there were no left-handed kids. Social contagion is the only explanation for as to why there are suddenly so many left-handed kids today, especially since many of them are boys and not girls.