That's a weird coincidence, because I forgot to fix a script error in my game and it turned into a chocolate souffle.
If you want to give this a propper shot, you gotta get things organised. Firstly, decide who's better at maths, and who's better at art. Now, both of you share gameplay ideas, but it's your maths brain that should worry about game logic, AI, collision etc etc, and your art brain should be doing lots of sketches and as much computer artwork as possible, most of all practise modelling and texturing, because that's the bare bones of the game art - perhaps your art teacher would let you guys do some concept stuff for your game, a concept sketch is an absolute god send when making 3D models.
The important thing is to keep working when not in class, you should both have pretty specific jobs to do and a lot of work to be done, so get your finger out
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Build the game design brief during math and english, perhaps collision detection maths is something your teacher could help you with - probably more usefull than fractions and all that rubbish anyway. Formulate a storyline during english. The thing is that you could very easily get in trouble with your teachers, or worse, get your teachers in trouble - so try and make the best use of the class your in if you must work on your game during school. It'll keep your teachers sweet too if they think your actually learning something practical through their subjects.
Van-B