This research project explores the overall effects that GeoGebra has on students' learning in mathematics. More specifically, this research demonstrates the effects GeoGebra has on student achievement scores, students' critical thinking/problem-solving skills, and students' engagement/motivation. In this research, two groups of high school geometry students from two different years were used to determine students' achievements and understanding. Students in 2018 used traditional teaching practices while students in 2019 used GeoGebra as a means of learning mathematics. The scores were taken from teacher made assessments and reported as averages from both years. In addition, observations and a survey were used to determine how GeoGebra affected students' critical thinking/problem-solving skills and their engagement/motivation in the classroom. Overall, GeoGebra showed an increase in student achievement scores, critical thinking/problem - solving skills, and engagement/motivation. Therefore, GeoGebra plays a major role in the teaching and learning of high school mathematics. This research project also aims to give teachers the confidence in how to use GeoGebra in their own classrooms to further develop students in the areas of student achievements, critical thinking/problem - solving, and engagement/motivation.