"Bored" as the reason that a student is underperforming is almost always bs. If you're so smart then just perfect the material and ace your tests. It should be exciting not boring.
I went to a magnet high school. The very smart kids have a lot of fun running circles around everybody else.
Some non-exhaustive examples:
1. Bored because they already knows the material.
2. Bored because the particular in-class activities are not engaging but they'll make more progress at home.
3. Bored because the entire subject seems like pointless memorization.
4. Bored because of a neurochemical issue.