You may be asking yourself, "geez, I wonder what he's replacing all that soda with at school."  I'm glad you asked.  I'm taking a concentrated batch of decaf iced tea in and mixing it with a large mug of ice water and artificial sweetener.  It lasts me a lot longer than a can of coke and must be better for me.  
As for effects of such a shift, I haven't had any headaches, but I have been a little on edge at times and a little sleepy during the day.  On the other hand, I've been sleeping like a baby at night, so I'm pretty happy for the decision.