As a general rule, the attention span of boys tends to be shorter than that of girls. Obviously, this varies with each child. There are more boys who suffer from ADHD.
Even boys who have wonderful powers of focus still have a tendency to bounce, fiddle with objects, look around, and generally want to be on the move.
Fortunately, it is possible to promote a healthy environment for your boys which will be more conducive for their homeschooling.