First, as stated above, who thinks this is even worthy of studying? Not having statistics before me I would hazard a guess that eighty percent of teens drink at least one or two sodas per day. Now you have to decide what constitutes heavy drinking. If it is anything like alcohol studies, three per day would mean you are a raging alcoholic. I would guess that based on those types of research, three cokes per day constitute heavy use. I personally don't believe that constitutes heavy use.
Now, there are two things that can be said when you begin to study things that can happen. You either are above the line of a supposed norm or are below the line. Unless there is a significant swing either way, there is not much that can be said to draw a conclusion. I think too often studies proclaim one way or another a correlation that has little statistical significance. (The article I read did not say what the statistical significance was). One could make an argument for virtually anything if you look deep enough.
Another thing that comes to mind is the saturation of this product in American society. Soda is so prevalent it would be extremely difficult to determine it this was a predominant factor. I could pick any number of products that have this type of saturation and proclaim some similar statement. I proclaim that teens who heavily listen to music on iPods get average grades in school. Well, what does that mean? Some would make the correlation that iPods have a detrimental effect on teens. But, more likely iPods don't have that effect but teens simply put off doing the studying they should be doing. That effect could also be attributed to television or video games or any other number of tech devices.
Unfortunately this type of study does nothing but find a small and meaningless statistical aberration concerning two unrelated items. It could also mean that teens that heavily drink sodas also drive faster than those that drink orange juice. It means nothing except to those who proposed this study because they now don't have to go out and find meaningful work, and I'm sure my tax dollars got mixed in there somewhere.