The purpose of this study was to examine the impact of student perceptions of the classroom motivational climate on engagement and academic achievement in secondary STEM courses. Additionally, the mediating effect of students' ease of the course perceptions on the relationship between engagement and academic achievement was assessed. By better understanding the relationship between students' perceptions of the classroom motivational climate and engagement, more effective instructional and curricular decisions can be made to address needs in STEM education. The quantitative causal comparative study was conducted at an urban secondary high school in the southern United States. Three questions were addressed using path analysis. The first two questions explored the relationship between students' perception of the classroom motivational climate, engagement (behavioral for question one; cognitive for question two), and academic achievement. The third question examined the mediating effect of students' ease of course perceptions on the relationship between behavioral and cognitive engagement and academic achievement. Data was collected regarding student perceptions of the classroom motivational climate (empowerment, usefulness, success, interest, caring), behavioral engagement, cognitive engagement, and ease of course. For the first question, a significant relationship between usefulness and behavioral engagement was found. Additionally, behavioral engagement was significantly related to academic achievement. For the second question, a significant relationship was found between empowerment, usefulness, and interest and cognitive engagement; however, cognitive engagement was not significantly related to academic achievement. Model fit indices were acceptable for both questions. For the third question, students' ease of course perceptions appear to have a mediating effect on the relationship between behavioral and cognitive engagement and academic achievement. The study results provide evidence for the nature of the relationship between student perceptions of the classroom motivational climate, engagement, and academic achievement and the mediating effect of students' ease of course perceptions. Equipped with this understanding, educators can make instructional and curricular decisions to increase students' motivation to engage. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]