Mr . : There are two things that you'll need to know .   What are they ?   Mr . : The school has three lunch periods , and the kids are divided into three groups to go to lunch .   Wow !   Mr . : Furthermore , when you are dismissed in the afternoon , you will be divided into two waves .   Two waves ?   Mr . : 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 . 