In addition to telling the parents/teachers about it and putting it in the local paper (and the school paper...most offer ad spaces to help fund their publication costs), you should also consider talking to the principal/superintendent. You may be able to get clearance to have flyers or business cards put in places like the guidance office or around the halls.

What grade level are you considering? If it's high school, you might have to jump through a few hoops and prove yourself to them to be a reliable source for students, but if you also include universities/colleges, then it's a lot easier to spread the word.