You can't take GCSEs early at NLCS except in your second language (ie Urdu, Mandarin, Japanese if you speak it at home) and only as an external candidate. There are so many ways of getting extra help at the school that outside tutoring is pointless. If a girl just 'didn't get it' in lessons, they can meet with their teacher or just walk into the department office and ask any teacher at any time. Or, they can see a peer tutor or even ask their classmates. One of the amazing things about the way they are taught to learn at NLCS is that the girls can explain the concepts to eachother. DD1 actually gets very excited when a younger girl asks for help. So, no, you don't need tutoring outside.
My daughter was at NLCS and had got in on a scholarship - she did not get any extra tutoring and neither did any of her friends.
I know how NLCS works - my comment was about general tutoring as mentioned in an earlier post. Lots of our students choose to carry on as their schools allow early GCSEs.