Using socio-scientific issues (SSI) in the science learning environment can promote student motivation to learn and make learning experiences more meaningful. Embedding model-based reasoning opportunities in science lessons can promote substantial science learning. However, how these both work together to promote science learning is a little studied area. We focused on this area by exploring if and how model-based reasoning supported 3rd-grade students in considering complex causal interaction patterns. We co-designed, with four 3rd-grade teachers, a unit on ecosystem interactions using an approach we call model-oriented issue-based learning. The modelling and issue lesson sequences varied across classrooms. In two classrooms, students wrote their positions on a prairie restoration issue, then model-based reasoned about interactions in an ecosystem before re-considering their position on the SSI. In the other two classrooms, students wrote their position on the SSI, participated in an SSI lesson, then rewrote their positions. Students from the two classrooms that model-based reasoned between SSI writings showed growth in their consideration of interaction patterns, while students from the other two classrooms did not. Implications suggest model-based reasoning may support students in considering complex causal interactions while the issue provided a context to reason about these issues in a familiar and relevant way.