At the Mt Pleasant School, where did Essie Mae Spent 3 or 4 hours a day?

From the text:

The day after Reverend Cason yelled at me, I asked to be excused. While in the toilet I thought to myself, "I can stay out here all day and he won't even know I'm out here." I began to spend three and four hours a day in the toilet and he didn't even miss me, until a lot of other kids caught on and started doing the same thing.