At the beginning of GTF, the 7th Grade do not know Dimitri Rascalov, and will not do anything if Dimitri goes to the 7th Grade territory at school. After the mission "...The Note", 7th Graders will start teasing Dimitri about liking Salvador, and keep following him around until he leaves. After "Salvador Sends His Regards", they become really hostile to Dimitri, not letting him in their territory because Salvador does not want to be bothered by Dimitri. Then, once "That Special Someone" is completed, they stop being hostile and welcome him to their territory. You have a respect bar that shows how much respect you have from the 7th Graders. Complete missions and side missions to increase the respect so they can be non-hostile to you early.