This document proposes a classroom action research study to investigate enhancing student learning outcomes in mathematics through a mastery learning approach at SMPN 15 Bengkulu City. The study aims to 1) describe the mastery learning process and 2) determine if it improves student mathematics learning outcomes. A literature review covers definitions of learning, step-by-step learning, mastery learning, and implementation strategies. The hypothesis is that applying mastery learning correctly will improve learning outcomes. Data collection techniques, research instruments, and analysis methods are outlined. Success indicators include individual student scores of 70 or higher and over 75% of students meeting the threshold.