My DS3.5 loves to do 2 digital addition mentally when he was just 3, now he didn't want to use the mental effort to do additions, and like to guess (e.g. 56+35 he said should be 8x or 9x). I am so want to ask him to think rather than guess, but d guessing is also a math skill :P
Sometimes i don know if it is time to let him take a rest or time for learning sth new as when he finished memorizing the multiplication table (he also understand it), he is so excited and said, "yeah, I can start learning division now!
Anyways, i think it is really normal for a kid as this young age to "not in a good mood" to do their work in school, especially test.
I remember that when I was in elementary school, I am really good at Chinese writing, but I did fail in one exam. It is bc i want to correct a word using the eraser but end up making a big hole on the paper that I cannot write anymore, and too nervous to ask for another paper :P. When we grow up, we can't remember how well we did the exams in the childhood but certainly remember the time we fail,and it is not a bad memory hum:P
