Being bored to tears is a good enough reason for anyone (child or adult) to exhibit odd behavior. Maybe the situation at school is giving him lot of stress and sets off the bouts of odd behavior...
My child will not talk about his day when I ask - which is mostly as soon as I pick him up. He usually has had a really stressful and exhausting day and just cannot recall anything at that time and I have come to realize that even asking gently or cheerfully annoys and agitates him because it is an added stress to refocus his brain on something when he is just ready to unwind.
I later figured out that his school has PE 45 minutes before dismissal every day and he plays really hard - he is an intensely competitive athelete that he exhausts himself competing and exerting himself.
Later on in the night, when he has eaten, rested, attended an enrichment activity or read a book, he is more inclined to talk - provided there are no distractions. Then he tells me what happened in class, what the teacher said about things and the interactions he had with other kids at recess etc.
So, one strategy would be to wait until your child is in a talkative mood or when your child brings up an incident that occured at school to slip in questions of your own.
And knowing the routine well is an advantage so that you can ask specific questions that require a simple yes/no answer - for e.g. if today had a spelling test, then you could ask if the teacher asked him to spell a certain word on the spelling test and it makes it easier for the child to recall the answer and say "yes".
And the best opportunity to address questions on academics is when we review the paper pile from school and homework. I ask him to explain his work to me and sometimes pretend that the subject matter is beyond my comprehension and ask him to teach it to me like a teacher. He enjoys using a whiteboard to write out stuff and teaching them to me.
My DS6 is a talkative guy when he is not stressed out or when he is relaxed. Is that so in your case too?
