DS 6yrs has been told where and how to wait for me after school since the start of this school year. If I am walking I will find him, but otherwise he is suppose to check by the main fence. He is suppose to play near that area if I am not there until he see`s me or if he see`s me he is to come out.
I try to park as close as I can to this fence and I wait in (or outside I had to park a bit further from the fence view) the car. I do this because I have a small baby who typically is finally having a much needed sleep and wakes up if I take him out of the car. Its gets hot in the car though and that wouldnt be much of a problem if we were just waiting a few minutes for DS 6 to come straight out of school and get in the car buthe doesnt . I have told him numerous times what the plan is and why its important for him to come straight out and look if Im there, but he preferes to play with friends and dosent bother looking at the fence if I am there - hence me getting very grouchy with him when after 10 - 20 mins of waiting I have to go find him

Its been a whole term now, and this as well as a few other rules that me and DH keep telling him it seems nearly every day, he just doesnt listen or remember. Its so fustrating and Im sick of it and feel bad for going off at him. I hate feeling like the crazy mumma, and last week when I was telling him off on the way home about not coming out after school (I had specifically told him that morning he had to cause he had an after school activity which he has every week) he pretty much ignored my fume and told me that I was just being angry for no reason - ie; he thought it was all my own issue.

What should I do?
How should I discipline him if he keeps doing this?
Am I expecting too much of a 6 year old?