We have a gated lot with entrances on two sides; think of an L shape. Before dismissal the exit gate is closed. You can go in through the entrance and all cars line up in the same direction (facing the exit gate) and stop engines. The entire lot fills, except for the striped section closest to the fence that is a fire lane. You can get out of your car if you want to, or stay in it. Lots of people get out and stand with the door open so that they can socialize. Parents of K and Gr1 students must claim them at the school doors, so they walk over there.
Just before the dismissal bell rings, the entrance gate to the lot is closed, and no cars may move. At dismissal all kids older than Gr.1 can just go to their cars. The little guys are quickly walked back to cars by parents and settled in. Engines may be started, but cars do not move until 10 minutes after dismissal, when all of the kids are already in the cars. When that time comes, the duty teacher opens the exit gate and begins directing cars out of the lot in rows starting at the fire lane (they are packed in so tightly that there is no other way that they can move -- you have to wait for the car in front of you to leave.)
Children who walk home go out via a sidewalk directly to the street; they don't enter the parking lot. If your child is in aftercare you do have to go to the classroom and sign him out; both parking lot gates are left open after the dismissal routine is finished, so at that point you can park in any open marked space.