Re: Overtones on student alto?
You absolutely can do overtones on a student model saxophone. In fact, they generally speak fairly well on a Yamaha 23 alto.
Blowing overtones is not only a great exercise for developing your altisimo register, but its great for developing a good tone and for learning control of the instrument. Almost nothing teaches you proper embouchure, support, and airstream control like blowing overtones. I recommend overtone exercises for anyone who's mature enough to do practice it correctly. Also, check out Dave Liebman's book, "Developing a Personal Saxophone Sound".