The sessions would be highly dependent on what the student requires. The great strength of 1-on-1 tutoring is the personalisation of eductaion to suit the specific needs to the student. My position would be to support what the student is being taught in school, reinforcing the most important ideas, while, when appropriate, allowing the student to see beyond what they've grasped in school to help them see the bigger picture. The key with teaching both chemistry and maths is to boil down what can seem quite complicated and arcane to simple principles which can then be built upon. This is something I really had to learn during my undergraduate teaching, in which I taught the Quantum Chemistry supplementary subject at Oxford. This required very careful and thought out explanations of incredibly complex mathematical ideas to allow the content to be accessible to the still very bright students. Teaching A level maths and chemistry requires a similar approach, although the trick, of course, is to adapt the content to the knowledge base of the student at the time, and to be able to relate what is being learnt to things to which they can relate.