This question does not at all pertain to ghostwriting. I believe it is more about cheating the system. Just because someone is able to bribe a cop to get out of a speeding ticket doesn't mean it should be acceptable. There are laws and standards that are established by society to improve the whole.
I would be willing to bet that each educational institution has specific policies and guidelines pertaining to this very topic indicating that any student involved in such activity would be expelled. I have two kids in high school, and I have actually signed a document that specifically addresses this very issue and requires both the student and the parent to acknowledge that this policy exists and that such activity will not be tolerated.
This site is supposed to be about helping people improve their writing skills. This question is NOT asking how to improve writing skills, it is asking how to improve cheating.
This question would be similar to someone going over to the Gardening SE site and asking how to improve their marijuana crop. Sure it's a plant, and sure it's a question that pertains to gardening, but it is a question about an activity that society in general would NOT recognize as legal or acceptable.