This paper explores the relationships among attitudes toward mathematics, teaching, and academic achievement in mathematics. Based on the contextual and social nature of academic self-concept, two complementary studies are discussed. The first study from the northeastern United States examined the relationships among these variables in 84 high school students. A second study from southwestern Nigeria examined how teaching approach can engender changes in student achievement and attitudes toward mathematics through the analysis of 36 preservice teachers associated with 830 students. Instruments used included the Program for International Student Assessment, the June 2012 New York State Integrated Algebra Regents Examination, the Student Mathematics Attitudes Questionnaire, and the Student Mathematics Achievement Test. Analytic methods included descriptive statistics, correlations, linear regression, and analysis of covariance. Together, the research supports the link between attitudes toward mathematics and academic achievement and suggests that teachers can improve student attitudes toward mathematics based on their teaching approach.