The drop off and pickup at school is critical for maximizing embarrassment.

DROPPING OFF: They will insist on you not stopping right up front but to let them out a little bit before so they can walk up alone. Do so. But once they get near the front creep slowly past them in the car with the window down and loudly tell them bye and to have a good day. Bonus points if you use a childhood nickname

PICKING UP: Arrive early and wait near the front. Have the windows down and be ready. Once they emerge and walking out queue up the music you had ready and play it at a rock concert volume ensuring that the child can hear it. Watch them scramble quickly to the car to make you stop. Be creative, Old Disney songs or theme songs of elementary age cartoons work well. Bonus points if you lock the doors and they have to stand beating on the car door telling you to stop