The purpose of this study was to investigate selected goal-setting as a predictor of mathematics performance among students in public secondary schools in Kisii Central Sub-County, Kenya. The study was guided by the Social Development Theory (1978) by Levi Vygotsky and the Theory of Education Productivity by Walberg (1981). The study employed the Solomon Four pretest-posttest two group design with post-test only control design. The study population included 1665 form 3 students and 41 form 3 mathematics teachers from public secondary schools in Kisii Central Sub County, Kenya. Purposive, stratified and simple random sampling technique was used to select the participants. The sample size comprised of 360 form 3 students and 11 form 3 mathematics teachers. Questionnaires were used to collect quantitative data while qualitative data were collected using interview schedules. The normality of goal-setting was established using the Shapiro-Wilk test and was established at Lilliefors significance Correlation of value .961. Trustworthiness of qualitative data was ensured using Shenton (2004) criteria for trustworthiness. The study used descriptive and inferential statistics to analyze quantitative data while qualitative data were analyzed with the help of the thematic framework. The findings revealed a statistically significant positive correlation between goal-setting and mathematics achievement. The study further established that students who set goals performed better in mathematics than their counterparts who did not set goals. The study recommended that universities, which train secondary school teachers, should include aspects of goal-setting as a self-regulated learning technique in their training programmes.