I do see where you are coming from ,and playing in band myself i am totally behind what the county council is trying to do.
Hazarding a guess here i would say the scheme is very similar to the essex music school initiative. Your son would be responsible for teaching a number of students probably once a week at one school, and then maybe on another day at another school hed teach a different lot of students.
This would probably be under the guidance of the school teacher designated in charge of the system, who would most likely advertise your sons tuition in the school and he can then sign up the students he'd teach. (this would obviously happen in as many school as he was working in at any one time)
if he must teach only 10 lessons a term it would work out as him probably only tutoring one student on any given session ( hence the money hed be making for one on one work) and lessons would take place once a week for most of the school term.
hope thats a bit more helpful if in doubt call up the county, they will be happy to help as they are normally used to people moaning about contracts!