I notice this is often the case for the first few grades in Elementary School. I always knew boys were more...hectic, but I didn't expect to see such a huge difference. Out of all the students I've taught in three years, I can only remember maybe 3-5 girls who were troublemakers. While among boys, I think at least 20% have had some kind of behavior problems.

What is the reason for such a huge difference in behavior?

Social conditioning. And this goes for most of the world. We don't notice when we're kids ourselves, but when we're adults, and observing, it's so apparent what boys are permitted to get away with. Most stuff boys do, girls would be shamed for doing the same.

This. I learned in 1976. :)

I notice this is often the case for the first few grades in Elementary School. I always knew boys were more...hectic, but I didn't expect to see such a huge difference. Out of all the students I've taught in three years, I can only remember maybe 3-5 girls who were troublemakers. While among boys, I think at least 20% have had some kind of behavior problems.

What is the reason for such a huge difference in behavior?

Another factor is the lack of male educators, especially at the younger levels. Based on my experience women tend not to be as stern with male students, and this can amplify male behavior until they are 'shockingly' put in place by their first male teacher when they are like 14.

Boys and girls have different brains and biology.  I thought that was obvious.  It's normal for a boy to be rambunctious and wrestling with his buddies.  Of course you always have to not let things get too far out of hand.  But simple stuff you can just get a kick out of it and laugh it off.  Girls tend to be made differently.  Though girls can tease each other and play fight too in their own way and some may talk a lot in class as well. 

*slap forehead*

Another factor is the lack of male educators, especially at the younger levels. Based on my experience women tend not to be as stern with male students, and this can amplify male behavior until they are 'shockingly' put in place by their first male teacher when they are like 14.

I'm not sure that's a massive factor though actually. I teach at an elementary school with mostly male teachers and the boys there are also rowdier than the girls

*slap forehead*

You can hate it but it is true lol. People forget that we're just animals under all our pretenses, and we're evolved purely to do animalistic jobs like hunting, foraging, protecting and copulating. It's a fact that human males are evolved to take the more violent roles in the animal world and that is reflected in the hormones they get.

Even in the few matriarchal societies in the world, males still fulfill these roles.