Considering how busy and annoyingly noisy the train was this morning, I think in my part of the country it is indeed the first day of school, but since I'm not in school, I don't really follow when the school ends and starts in which part of the country (it's split in three parts, which are sort of overlapping but not completely, to avoid too many traffic jams from people going on vacation )
I was out before the time on which children of lower ages would be cycling to school, so didn't really notice, but no, there's no specific tradition. Half of the children is going to school with a "fuck, vacation is over and life sucks" kind of mood, the other half is going all excited to share their vacation stories for a day and then get into the "is it weekend?!?!" mood just like any regular school day