FFJ, I just got into it with my first grader about those same questions/answers. My wife, who's a teacher, said one of her co-workers had a pretty good explanation for that type of answer. Basically, they just got done with a full day of school and don't want to talk about it. It's like asking an adult how their day was as they walk in the door.
I'm not saying this is a one size fits all answer, but it made sense.
Interesting info, thanks.
Granted, I'm asking my SS on the weekend (saturday or sunday, since those are the only days we ever see him), but I guess he still may not want to rehash it. He is very different than I ever was as a child, so it's hard for me to know what's "normal". I used to fight with my mom over whose turn it was to talk...I don't shut up.