I'm GATE coordinator as part of the fieldwork experience component of my master's degree/admin credential program. My wife actually held the position in our district last year, and "encouraged" me, in only the way wives can, to volunteer this year. I'm not getting paid any extra, although I suppose I could get the hourly rate for O.T., but I'm doing it for the experience. This year, anyway.
I see the same issue in some of my honors classes, with GATE kids who don't apply themselves. I don't know if it's because they're not being challenged, they don't want to be challenged, they're used to being successful with trying too hard, or if they don't think it's cool to be smart anymore. Unfortunately, despite my lofty title of GATE Coordinator, I'm no expert in GATE students or getting them to perform to their potential. The instructor of the class I'm taking now, though, suggested GATE contracts; students and parents agree to a certain level of performance necessary to remain in honors classes. GATE parents tend, I think, to be more involved than the average... Threaten them with being kicked out of the honors class, they may pressure the kids to do what they need to do to be successful.
Or, they may not. You may just get more parent phone calls and complaints to the principal. I don't promise success here.