GCSE Tutoring for children aging from 11-16 (Maths and Science)

I've completed my GCSE exams and am now going to start my A-levels, (picking Biology Chemistry and Maths), and I'm looking to teach children aging from 11-16 that are going to be doing their GCSE's. As I have just finished my GCSE exams, I have first hand experience of what comes up in exams, exam patterns for possible topics in exams, and techniques used in exams. Also techniques in how I can teach the students so as much content as possible, is retained for the exam, to maximise their marks and grades.