"Teaching math to secondary school kids; volunteering" - extracurricular activities

Hello,
I'm an international student, but please be as harsh as you can.
Any comments and critique will be welcomed.

Instruction: Briefly elaborate one of your extracurricular activities in high school.

Two years ago I was one of volunteer high school students to teach math to secondary school kids. After a few days of teaching, I realized they couldn't solve complex problems because of their lack of knowledge in basic math. I saw that it was essential for them to understand where their weak areas were, even though it meantasking for help and revising materials from several years back in their education. However, not all of them were willing to ask for help and show, as they thought, their weak areas in math and many resisted to. After a few experiments, I came up with a simple game to learn math. Taking in account they were still kids, learning math playing games made them feel more comfortable with each other and easy to learn together. Not all of them became excellent mathematicians, but, I believe lots could keep up with their more accomplished classmates, while I felt having helped someone to understand and enjoy math.

"To organize the teaching process and to choose a method,I had to find out where each student's discomfort with math began."

"This non-traditional method brought a better understanding of children's thinking" - rephrase this part

"Not all of them became excellent mathematicians, but, I believe lots could keep up with their more accomplished classmates, while I felt to have helped someone to understand and enjoy math." - This ending is quite ackward! Try something like this

"Not all of them became excellent mathematicians, but the majority could keep up with their more accomplished classmates. This activity made me feel to have helped someone to understand and enjoy math."

I need more improvement in terms of grammar. Any help or suggestions will be good.
Do you think that I need to put more emphasis to what I've learnt from this experience? Or maybe this description is okay?

secondary school students