I completed the South Australian Certificate of Education's Mathematical Studies and Specialist Mathematics streams in Year 11 of high school, running on a fast-tracked curriculum. The course covered algebra fundamentals, differentiation and integration, trigonometry and trigonometric functions, introductory statistics and probability, and some work on differential equations, all of which I am highly comfortable with. I frequently volunteered to provide peer maths assistance during a lunchtime program where I normally assisted younger students. I'm continuing to learn more mathematical techniques and concepts in my undergraduate degree such as mathematical modeling, engineering-focussed probability, and linear algebra.
I like to work with a student's existing curriculum and tend to find that a lot of difficulty results from past fundamentals that were rushed or half-understood. Focussing and reiterating these fundamentals outside of the classroom where there's no necessary pace allows the proper attention to be given to a student's individual rate of learning according to their strengths and weaknesses. For example, learning to be comfortable with fractions relies heavily on being comfortable with multiplication and division but if the student is less prepared in this area they may believe they are simply unsuited to the new concept. I like helping fellow classmates as a way of helping myself understand new material and reinforcing my own fundamentals, but I believe I'm most suited to helping with concepts I've been using routinely for a long time now (namely secondary-level mathematics).