This document summarizes a presentation on developing thinking through high school mathematics. It discusses how student achievement declines from elementary to high school and calls for changing mindsets. It provides examples of engaging students in high school math concepts like algebra, geometry, and problem solving. These hands-on examples from schools in Singapore, Indonesia, and elsewhere encourage students to make sense of formulas and collaborate on problems. The conclusion is that math can develop thinking beyond just content if taught in this way. International test scores are also presented showing Singapore performs among the highest in math achievement and affect.