Eighth-grade students who are placed into Algebra 1 but fail end-of-course exams may experience lowered grade point averages (GPAs) and loss of motivation for math or avoid taking advanced mathematics courses in high school. Middle-achieving students present challenges in terms of mathematics placement. Self-efficacy theory and locus of control theory suggest the noncognitive traits mathematics self-efficacy (MSE) and academic locus of control (ALOC) are associated with mathematics achievement and could predict achievement in eighth-grade algebra. The purpose of this quantitative correlational study was to examine whether MSE, ALOC, and prior-year State of Texas Assessments of Academic Readiness (STAAR) mathematics score predict achievement in eighth-grade algebra among middle-achieving students in South Texas more accurately than prior-year STAAR mathematics scores alone. The sample included 111 eighth-grade algebra students in a large suburban school district in South Texas, whose scores on the previous year's STAAR mathematics exam fell between the 25th and 75th percentiles. MSE predicted meeting grade-level standards (R[superscript 2] = 0.229), performance category (R[superscript 2] = 0.327), and percent score on the NEISD Algebra 1 Benchmark exam (R[superscript 2] = 0.317). ALOC was not associated with achievement on the NEISD Algebra 1 Benchmark exam. These results suggest that predictions of achievement in eighth-grade algebra for middle-achieving students were improved with the addition of measures of MSE, but not ALOC. Suggestions for future research include developing a mathematics locus of control instrument and broader studies exploring the relationship between MSE and achievement in eighth-grade Algebra 1. [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.]