Open-ended mathematical tasks provide great opportunities for students to engage in authentic mathematical practices, such as conjecturing, generalizing, and justifying. Supporting students in open-ended tasks can be challenging. Appropriate scaffolding of a task has been linked to more opportunities for student learning and better student solutions (Mayer 2004; Henningsen and Stein 1997). But what does effective scaffolding look like? The JAGUAR project (Justification and Argumentations: Growing Understanding of Algebraic Reasoning) was a collaborative research and professional project that investigated justification in middle school classrooms. Each teacher implemented four justification tasks over one school year. After discussion and reflection, those same tasks were implemented a second time the next school year, with some modifications. The goal in the first year was for students to discover patterns in the relationship between scaling side lengths and the resulting area. In the second year, the math objective shifted toward explaining why the relationship held, which improved student justifications. The tasks were implemented with different eighth-grade students from year to year, but the school and context remained the same.