You think these kids are stupid or something? They know damn well that there is a huge difference between pot and smack, for instance. And you'd better believe that they know when they've been lied to. So what do they do? Since they find the "information" they have been given to be at best suspect, more likely worthless, they experiment; they find out for themselves. Some of them learn the hard way. Some get hooked. Some get dead. Some kids who end up dead would be alive if they hadn't been lied to. Now, do you still think the drug-ed stuff is worthwhile?
P.S. One of the funniest things I ever saw in my life was in a "drug education kit" that a friend had, a county sheriff -- anyway, there were examples of what various substances and paraphrenalia looked like. Most of them were accurate. But the thing that was supposed to represent peyote looked more like a cake of soap with a flower design, and it had me rolling on the floor laughing. Oh well. Maybe you had to be there.
There's more discussion on the subject on E. Bear's (Mainline) Drug Page