Sorry I can't give you any advice. I don't blame your son. Second grade is too young to be getting homework!
Unfortunately, it is the way most schools do things right now. But hopefully that will be changing in the next few years. Parents need to realize the damage we are doing to our children by allowing the schools (and government) to teach to the test. Children are ending up in therapy, having breakdowns, developing eating disorders, getting headaches and stomachaches, and even committing suicide because we are failing them with our education system.
"Race to Nowhere" is a new documentary out that EVERY adult should see - parent, teacher, administrator, school board, everyone! Children are given too much homework and not enough recess. They are being subjected to stupid tests that they may or may not pass, but it doesn't really matter, because once the test is over, they forget everything they learned for it.
Children today are graduating without any critical thinking skills. They don't know HOW to think and problem solve, because all they've had to do is memorize and regurgitate information. But they (the students) will tell you that once they spit it back out, they don't remember what it is they have learned. They are just trying to get into college, and think that college is where you start learning. High school is just to get you there. I've heard elementary students say that their school and homework is just to get them into a good high school.
We are failing our children, and we all need to speak up and do something about it.
Sorry for getting on my soapbox, but hearing about an 8 yo crying over homework tends to make me do that.
Go online and find out how you can see the movie "Race to Nowhere". Then get involved in bringing about change. THAT is how you can best help your son.