New School’s studio teacher system is quite different from the other conservatories. During orientation students are evaluated on a set of minimum instrumental proficiency skills required for graduation, then either be placed “in proficiency” where he will be assigned a studio teacher based on his individual playing ability and needs, or he’ll test out. If he “tests out” of proficiency, he can choose from one of many, (20 or more), private teachers that are gigging musicians and teachers in the area that work more like private contractors than regular faculty. If I understand correctly, the student is responsible for setting up the lessons and scheduling with the chosen instructor once they have tested out of proficiency. After the first semester, students can split their lessons between different teachers on different instruments, genres etc. They can shake it up or keep the same instructor.
As for the other schools we looked at, some asked for a ranking of preferred teachers, some did not, and some only had one bass instructor so it didn’t really make any difference. In those schools, the assumption is that you’ll be with one teacher all 4 years, unless otherwise requested or some different arrangement is worked out at a later date.
If your S chooses New School, I’m sure they’ll help him through the studio selection or assignment process. At another school, he’ll probably be assigned to a studio that they feel will best suit his needs. I’m sure it will work out just fine in either case!