We have State Farm. My suggestion is to buy a beater car and have your son rated on that car. My sons car is a 2002 Buick. The insurance monthly on that car is less than $40 a month and that is the car he is rated on. He takes the car to school with him. Do you have the same number of cars as you do drivers?
I don't think that's how it works for most insurance policies. We had State Farm when our daughter started driving and even though the policy on her car was lower, they raised the amounts on our other two cars because she was added to our policy. So the amount assigned to your child's car may not really be the total amount that they are costing you.
For example, if you look at just the amount of my daughter's vehicle it works out to being under $80 per month. However, if you compare the total amount from what we were paying when it was just my husband and I on the policy, we are actually paying over $150 per month more.
But when I called in and told them the discounts were on the wrong cars so I thought they flipped things incorrectly - they proceeded to tell me no, that's just the way they do it now - they basically assign drivers and discounts to cars in the most expensive way now. They were basically treating it like DD was driving the expensive car with full collision, even though she never, ever did. There was no way to undo it. And no, they didn't feel like they needed to proactively provide an explanation to policyholders that their underwriting methodology had changed.
Yes, some companies automatically put the most expensive driver on the most expensive vehicle (that's what my parents' insurance did when my younger siblings were driving). Others will spread out the total and increase all the vehicles in the household. They justify this because in theory anyone on the policy could be driving any of the vehicles.