You stated that he got into alot of trouble in middle school. How is his behavior in the alternative school? My nephew was causing trouble in school, so they sent him to an alternative school. I was dead against this. I had the same prejudices that so many other people have. But, you know what? He turned into the model student at that school. My sister said that she thought they might have been thinking about the wrong kid, when they told her over and over what a joy to have in class he was. Now, he's just about to graduate, and is joining the Marines. This is the change that overtook my pot-smoking, trouble-making nephew in a few short months.
If your son is doing well in his school, maybe you should consider letting him stay there. If he's still up to no good, I'd give him an ultimatum. Straighten up in the school he's in, or move to the new school. Point out to him that he can do poorly at either school, and that he needs to give you a reason to believe this is the right school for him.