<![CDATA[Authentic sustainability contexts remain insufficiently integrated into mathematics instruction, limiting opportunities for students to connect empirical data, mathematical representations, and evidence-based reasoning. This study addresses this gap by positioning aquaponics as a sustainability-oriented context within Project-Based Learning integrated with STEAM (PjBL-STEAM), offering a novel learning environment for developing function graph literacy and mathematical critical thinking. The study examined the effectiveness of Aquaponics-Based PjBL-STEAM and explored the learning processes characterizing students’ engagement with these competencies. A mixed-methods embedded experimental design involved 126 Grade 10 students from Sekolah Adiwiyata Latansa Mashiro 1 Cipanas, Indonesia, assigned to Aquaponics-Based PjBL-STEAM ( ), STEAM with a scientific approach (n = 42), or direct instruction ( ). The Aquaponics-Based PjBL-STEAM group demonstrated the largest gains in function graph literacy, from to , and mathematical critical thinking, from to . ANCOVA indicated significant instructional-condition effects on function graph literacy, , partial , and critical thinking, , partial η² = .262. Qualitative analysis identified data-driven mathematical reasoning, construction of functional relationships, coordination of multiple representations, and evidence-based graph interpretation. These processes illuminate students’ connections between empirical data, mathematical models, and graphs, complementing the quantitative findings without establishing causal mechanisms. Overall, the intervention was associated with stronger development of both competencies, highlighting the potential of sustainability-oriented project-based STEAM for mathematics learning.]]>
