There were three primary purposes for this study. First, I investigated the psychometric properties of the Sources of Middle School Mathematics Self-Efficacy (SMMSE) scale (Usher, 2007; Usher & Pajares, 2009) with high school students. Validation for expanded use of the SMMSE scale was achieved by assessing the instrument's psychometric properties when used with a new population (high school and middle school students) in a different geographical region (suburban northwest). The second purpose is to further validate Bandura's (1986, 1997, 2012) theorized model of how self-efficacy beliefs are formed, which include mastery experiences, vicarious experiences, social persuasions, and physiological states. Third, the relationships between efficacy sources and other constructs included an examination of any differences that could be observed between boys, girls, white and minority students as well as ability grouping by placement in grade level courses. The sample included 1080 students from two suburban middle schools (n = 445 students) and three suburban high schools (n = 635 students), which were used first in an exploratory factor analysis of the 24-item survey. A four-factor confirmatory factor model demonstrated the best fit for the SMMSE scale, and was found invariant across middle and high school samples. As predicted, mastery experience was the strongest predictor of mathematics course, skills, and grade self-efficacy. Small or moderate differences were observed between gender, ethnicity, and ability level groupings. Results of the analysis verified the factor structure of the Sources of Middle School Mathematics Self-Efficacy with a new middle school sample, and also verified the factor structure was invariant with a high school sample. Overall, the items within the SMMSE demonstrated reasonable reliability and factor structure with a new group of middle and high school students and could be used reliably with secondary students. [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.]