The Bimbo Teacher route is one of multiple routes in Adventure High.
To access it, you must enslave Ms. Rack at some point and transform her into a bimbo.
Attend the second secret notes class while she's in her bimbo form and then change her back to normal.
Speak to her in her classroom and allow her to speak, then agree to help completely.
Again, speak to Ms. Rack - still in normal personality - for a scene to play out in which you can either make her keep her promise to help the student or help her.