Warner Brothers request form with instructions for seeking use of a clip or still. (It looks a little bit worky but hopefully somebody at WB can help you through the process.) Freedom Writers looks like it's owned by Paramount. That company directs folks like you to click on their Paramount Film Clip Licensing link which unfortunately leads nowhere (or at least it did when we tried it). We also tried to find a link for MTV Films, the co-production company but all our links for that lead, alas, back to Paramount. Perhaps you'll have better luck at the Freedom Writers website but we think you get the idea. You need to find some way to contact the owners. Once you do, plead for permission, and hope your request doesn't get buried on some paralegal's desk.
The Fair Use Argument. If you can't obtain permission, you may -- depending on the length and context of the clips -- be able to justify your borrowing as a fair use. The marketing aspect of your effort works against that argument but take a look at some of the audiovisual cases (scroll down to the Artwork and Audiovisual cases) to get an idea. As always, remember that fair use is a defense, meaning that a complaining copyright owner can drag you into court to defend yourself.