My little one has been doing it for about 15 months, both from the school district, through early intervention, and private as well. He is 2 years 10 months right now, and we have about 15 words we can understand. But, he is also autistic so that impacts how we do. Honestly, the speech therapy helped to put in the foundation and keeps the work going, but the changes we have seen have really been since November when he started a Qigong (She-gong) Massage through a trial here. They have a website where you can get information www.qsti.org. If you buy the book, it comes with a DVD and poster to show you exactly what to do. Really, its a program that you do at home, I do it every night for him. It takes about 15 minutes or so. The theory is that the energy gets stuck in the body, but the language center in the brain connects directly to the pointer fingers and a specific toe, but I don't remember which one. When the energy gets to the fingers and toes, it will let the language center in the brain work. The results have been amazing for us and all the other families I have talked to. I know the study has only been done on Autism, but the theory is sound for ALL people, and I know when it was done to me, I felt much better and more grounded.
I hope all of this helps and its not too much. But, like everyone else said, the progress your son makes depends directly on the work you do at home.