Kurzbeschreibung: Researchers’ decisions to work with particular theories and to employ certain research methods are neither prescriptive nor neutral. Hence, it is valuable to examine how the use of different research methods, may corroborate or expand knowledge of theoretical constructs and/or frameworks. Drawing on empirical results of three studies investigating relationships between students’ graph reasoning, graph selection, and attitudes towards mathematics and graphs, I offer three ways that mixed methods designs can advance mathematics education research. The first is to provide corroboration for theoretical frameworks positing different levels in students’ mathematical activity (e.g., a framework of students’ graph reasoning). The second is to test theoretically grounded hypotheses regarding relationships between different constructs (e.g., students’ graph reasoning and their graph selection). The third is to examine mediating relationships between constructs grounded in different theoretical perspectives (e.g., how students’ attitudes toward mathematics and graphs may mediate a relationship between their graph reasoning and graph selection). Yet, with these advancements also come caveats; when using mixed methods with larger data sets, there are tradeoffs to be made. I conclude with implications for theory and method.