Sinclair, this sounds like a wonderful idea because I have participated in such a program at the university level.
For example, I was selected by the department of mathematics because of my high scores within several mathematical subject areas. In this case, it was Pre-Calculus, Trigonometry, and Calculus. Next, the department paid each selected student a stipend to work as a teacher's assistant (TA) to support the lead instructor. These tutorial services was a university sponsored program and free to the students which took place throughout the year.
Thus, I have the following questions about your proposal:
a) How will students be selected to take on the role of being responsible for 3 other students?
b) What's the incentive for one student to teach another student? Stipend? Other compensation?
c) How are you planning to identify students that are in need of assistance? Working with colleges and universities?
d) From my experience at the university, one may need to become knowledgable of each colleges and universities assessment practices to better assistance the students prior to entering the university.
e) As a tutorial service, it may be a good idea to extend these services throughout the year. For example, a student does well on an assessment examination which puts them in a higher level course but this higher level course is simply a bit too much. Thus, you may want to consider broadening the scope of the service because your goal is to see the student succeed within their academic career.
f) Is this an online service or an in person service?
Well, these are the questions/comments that I have at this time and please feel free to post followups because this is very very project.