Being very interested in tennis and having potential to be very very good to justify special training are two very differnt things.

How old is the kid, how much has he played etc. are some things to be considered and then obviously the cost.

A lot of tennis stars do start young and spend a lot of hours on courts but that could also be initially handled by normal schooling being a tennis club member, and taking several hours of professional coaching on the side.

How he improves and how he measures up against other players is what I would look for in deciding how far his tennis playing may go.

A good yard stick would be if he progressed quickly to be able to play against and beat club/school players older than him by several years, then there could be potential to consider being involved in a special tennis school.

Meanwhile, you could always look at contacting the Tennis Professionals body, might go under something like Tennis Australia or google that for links and they may have independent recommendations or a rating system for schools/coaches.