Let's see...

Kindergarten (1) + elementary school (8) + high school (4) + university (4)

16 without kindergarten, 17 with (yay--I can do math!).

I also did a stint in two different preschools/daycare schools. That would be another three years.

All in all, I spent every non-holiday weekday (that I was not ill or on vacation or had some other commitment for) during the "school year" at an institution of learning of one kind or another from age 3 to 22.