How much you can control an independent contractor is a very difficult question to answer
IRS Form w-9 should be collected from every independent contractor paid by your homeschool organization.
Here's a great list of things to consider including in your IC agreements.
Is a hired director an employee of contractor of a homeschool band?
Can a homeschool organization offset a teacher's pay by giving her discount for her child to attend classes?
It's very common got homeschool co-ops and tutorial programs to ask parents to pay the teachers directly
Factors the IRS uses to distinguish between employees and independent contractors including the type of relationship between the worker and the employer.
Since so many homeschool organizations hire workers as Independent Contractors, it might be helpful to examine the difference between employees and independent contractors.