A Normal Teen Thing, but

So my son has after-school help in Algebra on Wednesdays. This was to be the 3rd week he’s gone. Last week I waited till he was supposed to call me, per his guidance counselor (which he didn’t, at least at work) to go get him, so I picked him up rather late. He kind of got on my case & said I should have just come at 3pm to get him like we originally talked about. So I said OK—that is what I’ll do next time.
 So this morning, I reminded him (as well as myself) that he had after-school help & that I would meet him at the school drop-off point at 3pm. I even said as I dropped him off, “See you here at 3pm!”
 3pm: I get there, he’s not there. I go in the school, he’s not there. I’m waiting…call work to see if he called (no); call home to see if he called (no). Then I tried home a few more times in the hopes of reaching my daughter, who was to be dropped off by her friend’s mother, no answer. Finally, 3:20pm, I call & he picks up! He had completely forgotten!
 So when I get home to change the load of laundry, I told him how I rearranged my work schedule for him & I only had an hour (I moved my lunch hour). He said he was sorry. I said I knew, but I was still mad.
 They got their report cards today. I haven’t seen it yet, but will later sometime. I wonder if that threw him off. Or if this was just an ordinary blip. Argh.