I'm fifteen too, (white male if that matters)
First Point: Either your not getting enough sleep, doing a technique wrong, have ADD. I don't know there could be many reasons for why you can't pay attention. Try to be open minded ( No offense intened, just couldn't word it any other way) and figure out what it really is. I now that school's almost out for me and i could care less about school right now.

Second Point: This is the one that got me lost for words..... Lucid dreaming is natural for some people. I've had them my entire life. I can concentrate (i have a 4.0 GPA in school), I get sleep. And if anything it will probualy help your brain figure out stuff because it's not just giving you random information.