This is a classroom action research. Classroom action research is an effort that researchers can make to improve the quality of the roles and responsibilities of educators, especially in the management of learning. The objective of this study is to improve learning activities and mathematics learning outcomes through the Aptitude Treatment Interaction (ATI) learning model for eighth grade students of SMP Negeri 2 Jatipurno, Wonogiri on academic year 2018/2019. The data collection methods are questionnaires, documentation of learning outcomes. The validity of the data use triangulation techniques. Learning Model Aptitude Treatment Interaction (ATI) with a discussion process with several study groups that have been grouped based on similarities in average abilities. Based on data analysis from two cycles, it can be concluded that this study has an increase in student learning activities so that it affects the learning process and student learning outcomes also have a significant increase. Learning activities Aptitude Treatment Interaction (ATI) Learning process This is an openaccess article under the CC-BY-SA license