The quality of curriculum resources and teaching practices can constrain or promote students' opportunities for mathematics learning, in particular, students with diverse language proficiency. The video study investigates 18 classes that all used the same curriculum resources aimed at developing 367 seventh graders' conceptual understanding of percentages to identify the interaction of quality dimensions, the enactment of given curriculum resources, and students' mathematical achievement (when controlling for mathematical preknowledge and language proficiency). Multilevel regression analysis revealed that three quality dimensions that can easily be supported by the curriculum resources ("Mathematical Richness," "Cognitive Demand," and "Connecting Registers") were on a high level, and their variance had no additional interaction with students' achievement. In contrast, the 4 quality dimensions that were enacted in the teacher-student interaction with more variance ("Agency," "Equitable Access," "Discursive Demand," and, in particular, "Use of Student Contributions") had a significant additional impact on student achievement. These findings reveal important insights into the implementability of equitable instructional approaches.