Half the days of the year ?

Hi~ What do you think of the phrase "half the days of the year" mean?

Half a day during a year ? It's confusing to me, with the combination of the phrase "each day".

Thanks for your help~

The vast majority of American children still attend schools that look much like the institutions of the early 1900s; they spend a relatively limited amount of time each day on less than half the days of the year sitting in classrooms with peers of roughly the same age.