My son is 8 years old. He is generally a good kid, but if he encounters difficulties with learning (homework or learning something new, or solving a math problem) he winds himself up, starts crying and -what seems like- turns his brains off . We can calm him down, but teaching him anything in the next 2-3 hours is impossible. Then he has to go to sleep, as it gets late and this happens quite often. It reflects poorly on his school grades. What is the best way of dealing with this?