I've always had the same problem. My grades have ALWAYS been average. School has never really challenged me, I felt I already knew almost every thing that those people were trying to teach me, at least when it came to subjects with words. In math, I never applied myself because I never believed in myself.

What you should tell them, I think, is that they KNOW that you've never had the best of grades, but that you will promise to not let any of your grades fall to failing or below average (D range) if they just let you toke when you need to, and not get on your back about it.

If they do flip out when you tell them that you smoke, I think you should tell them that you'll quit doing it in their house, or around them, that you'll never come home high, etc etc. That way, you're not completely lying to them, they'll know you smoke, but you won't let them know how much you really smoke, and they'll think you're doing okay with it.

Just make sure not to smoke all the time. Depression, suicide, and a whole list of other life-fucks run in my family, and over time I've allowed marijuana to turn into my panacea. Meaning, I use it for everything negative in my life. I'm depressed? Smoke. I don't feel good? Smoke. I'm bored? Smoke. I'm hungry? Smoke.

It goes on and on, don't let it happen to you, mi mano!