University winter break in Italy

I don't think the calendar of the Academic year has anything to do with crowds in Florence.
At the Univeristy of Florence classes start at the beginning of September and end at Christmas. They start again on March 1 till June 30 for the second semester.
During what you call breaks, are the examination sessions of all courses taken (January-February and July-August). Unless things have dramatically changed since my time at the University of Florence, Italian university students don't have the tradition of the American style spring break when students go and occupy entire beach towns in Florida. In winter, particularly around New Year's Eve, lots of young people like to go to ski resorts, so if you plan a trip to the Alps during that time, book early.
If you are looking for a time when there are fewer tourists in Florence anytime from November through March is a good time. There might be a few more during the Christmas holidays, but nowhere close to the Spring and Summer crowds. When Easter falls at the end of March there are more tourists during that week too.

The thought was that if that is semester break in Europe, there might be a flood of student tourists from other places in Italy and other countries then, making March perhaps a less crowded time.

If you want to avoid crowds in Florence, go in January. November may be very rainy, December has Xmas festivities, January is chilly - but not excessively so and there are few people around. Maybe also February. By the end of February or beginning of March crowds start to come again.

Thanks all. Your insights are helpful.

I wouldn't worry about crowds anytime between November and March.
Xmas holidays may be an exception, however it's not as crowded as Easter week or any time in Summer (although August in Florence isn't bad either).
If cold temperatures are not an issue I agree that January and February are the slowerst months.