There are two things that you'll need to know.
What are they?
The school has three lunch periods, and the kids are divided into three groups to go to lunch.
Wow!
Furthermore, when you are dismissed in the afternoon, you will be divided into two waves.
Two waves?
The school parking lot is not big enough for all the school buses to come in at one time. So only half the buses come in first to pick up the first wave's students.
And the other half come in later to pick up the second wave.