Hey Kendra,
Bobisue has a good point that the tutors would do well to give a presentation of sorts to the students in class. Your tutors need to be introduced to the kids in a positive light, in a way that shows how the tutors bridge the gap between teacher and student.
To answer your question directly: Nothing would convince me or any average student to ever go to something after school that is not required and called "homework club." Get real! First things first, you need a new name for your project. Choose something short, interesting, catchy, and cool sounding. Perhaps "High Five" or "Beat the System" or "Head of the Game" or "Keepin' it Real." The point here is that the name can be a help or a hindrance to your goal of getting these street smart kids to better themselves and their communities. It's just a name, but it can make all the difference.
You need to be creative here to get your target audience. Maybe give the kids a dollar to show up, and call the program, "Bribe to Better." Maybe get local rappers and bands to show up and play a set once a month. Try targeting select popular students to attend, because others will follow their lead. Get the newspaper to do an article on you guys, with some photos. Get people talking about it!
All your current ideas are good, the bonus marks, food, posters, etcetera but you're going to need a real good hook. All that stuff is icing on the cake, but you need to have a reason for them to be eating that cake. And let's face it, you're offering them the healthier carrot cake option of doing better in school by additional studying while every kid is already offered and guaranteed the triple layer devil's food chocolate cake option of getting the heck off school grounds and going to hang out with their friends and video games.
The core attracting factor will really be the tutors themselves. You guys need to focus on being cool, smart and outgoing. Your tutors will need to reach out and touch the lives of these kids, in class and out of class too. You're going to need to work hard and pull in the real tough cookies, the kids who are predisposed to automatically hating everything to do with school. And that's not going to be easy. But if you can catch those fish, even just a couple, then the other fish will follow suit.
Good Luck and remember to have fun!
-Mark
Additional Details edit:
Thanks for coming back to this question and answer conversation, Kendra. I'm glad the coordinating teacher and administrative personnel is so conscious of the tutors setting examples. You tutors are helpers who bridge the gap between teachers and students and are powerful peers who provide a visible and tangible way for the teens to peer into the positive possibilities of their immediate potential futures. Some will see that they can help others as well.
bobisue talked about another good point of making sure that the students understand that you're really trying to help them. Be it with homework subjects, fitting into a social activity, just chilling out and maybe being simply present and available to listen to random life problems. Some kids just need some human contact, maybe a hug every once in a while.
I hope the program keeps on evolving!