My reccomendation is to let the student pick the horn. Don`t get him something that he might not like. When he is ready for a new horn, he will let you know. He will also know what he wants, or he will be willing to research it. I reccomend letting him play a school instrument, or purchasing or renting a student horn, and when he starts to feel held back by it, encourage him to research the horn he wants. Let him talk to other trombone players, including professionals. In the end, he will pick a good horn for himself. After all, he is the one who will play it. Good luck to both of you.

There are lots of great student model horns out there. Kings are always great especially when you can get a good deal on them. 2B`s and cheaper 3B`s are great, solid long lasting horns, as well as Yamaha student models and Bach student models. But again, it should be something the student is happy with. If they aren`t happy, they will never get to the point where they are ready for that next step.