I found the job because my friend was working there. On the website, there is also a place to sign up. They do their hirings in the beginning months of Dec and June. They decide to interview you based on your SAT score so I suggest anyone who has above a 1400 (or equivalent on the new SAT) to apply.
Before the interview, they give you an SAT test to take home. They suggest you attempt to do it in the time imit, but it's okay to go over. They want to know what you know NOW. Before taking the test or even interviewing, I suggest brushing up on some SAT tricks by getting one of those Princeton Review books from the library. It's what you'll be teaching from, anyway.
The interview is a 5 minute presentation in front of a few people. Bring handouts and use the board. Use eye contact. Do not talk to fast. It's better that you have more material ready to present and not get to it than not prepare enough. Bring props.