How much should I charge as a private tutor?

You cannot claim your input actually achieved this or any of the other results you quote. As I said you need a DBS before you can start bringing people into your home. Tutoring sites are not very hard to get jobs with as teachers don't want to be involved in them.

I recommend you drop the tutoring idea until you are better qualified.

There a bit of misinformation flying around this thread! You do not need a DBS check to tutor, whether in your home or outside it.

Parents will want to see a DBS and you'd be foolish to tutor someone in your own home unless there is another adult there - you are risking all sort of accusations.
You are not exactly unbiased here ... this is an advert isn't it?