In most of the cases in schools its the teachers that catch the virus or at least the ones that show signs of it and then classes have to close. Some kids need more help than others.. some get on fine doing it at home with parents if possible but some never get on well without face to face learning from a trained teacher so it really does depend.
I volunteered in a primary school and you easily see the difference between those who can work independantly and those who can't. Some also don't get as much help at home than others so kids are generally better in school learning aslong as better precautions are taken. Otherwise its going to spread much easier.
This 2nd lockdown doesnt really seem like a lockdown because the majority of daily life is just as its been for the whole year anyway, most of us are getting used to going out less and only going to the shop when essential.