Even though the United States (U.S.) spends, on average, more money per student than most Organisation for Economic Co-operation and Development (OECD) countries, it continues to lag behind its international peers in mathematics achievement. This study, which responded to the call for educational reforms that improve the mathematics achievement of U.S. students, aimed to examine the issue of student help-seeking behaviors and teacher instructional practices as they interact to affect student mathematics achievement. The Programme for International Student Assessment (PISA) defines student help-seeking behaviors as the ways in which students have a propensity to depend on the knowledge and intellect of others, including both their peers and teachers, when attempting to solve problems. Because mathematics is perhaps the most difficult school subject, student help-seeking behaviors should be a critical component of mathematics learning and teaching. Unfortunately, the research literature is barren concerning this important educational issue. This study attempted to produce the first wave of empirical evidence and open up an avenue for future research in this less-charted academic field, with the ultimate goal being to use students’ help-seeking behaviors to improve their mathematics achievement. Using the U.S. sample of 15-year-old students from PISA 2012 (the most recent PISA assessment in which the main area of focus was mathematical literacy), this study intended to determine whether students’ help-seeking behaviors play a significant role in their mathematics achievement, whether this relationship varies from school to school, and whether teacher instructional practices contribute to the school-level variation. Due to the multilevel structure of the data, with students being nested within schools, a two-level hierarchical linear model (HLM) was employed in the analysis of the data. Multiple measures of mathematics achievement were used as the dependent variables for separate analyses. Student help-seeking behavior was used as the key student-level independent variable, while three teacher instructional practices were used as the key school-level independent variables. In addition, several student and school background characteristics were used as control variables. The findings from this study indicate that student help-seeking behavior has a statistically significant effect on all measures of student mathematics achievement, even after controlling for various student background characteristics. On the other hand, the study did not find statistically significant evidence that the effects of student help-seeking behavior on any measure of student mathematics achievement vary from school to school. Overall, the issue of student help-seeking behaviors should be considered a worthy topic to pursue in future educational research. From a practical standpoint, since students’ mathematics achievement is positively associated with their help-seeking behaviors, efforts should be made to educate mathematics teachers on how to encourage their students to be more proactive in seeking help in the learning of mathematics.