The short version is that LJ will give you (for the asking) a $30 gift certificate for DonorsChoose, which is a program that matches up schoolteachers with requests for equipment (etc.) and donors. You choose your project.
The catch is that you need to ask some time before 5 pm Pacific tomorrow.
Email to email@example.com and request yours. If you have no clue what to give it to (and the cool thing is that you can search by interest/location), I have a couple! (one in West Oakland, one in the South Bronx)