This book focuses on application of Active Learning strategies to develop students' level of understanding of Mathematics. Active Learning is a process whereby students engage in activities, such as reading, writing, discussion, or problem solving that promote analysis, synthesis, and evaluation of class content. This study was conducted in an international school in Bangkok, Thailand with two groups of students in Grade 9 High School Mathematics over 4 Quarters. The academic results (GPA) of students who learned mathematic through Active Learning were compared to the results of those who studied Mathematics in a traditional way. The overall pattern demonstrated a difference between average GPA of students in Active Learning group and control group implying that Active Learning strategies led to improvement of students' level of understanding of Mathematics.