There is a growing attention around the preparation of pre-service teachers (PSTs) as both learners and teachers of mathematical modeling. Current literature focuses on preparing PSTs as learners of modeling, and we extend current work by examining how PSTs integrate their understanding of modeling into the work of teaching. This study follows two groups of PSTs, concurrently enrolled in a modeling course and a secondary methods of teaching course, as they completed a joint unit of instruction in which they designed, refined and enacted a modeling lesson in a secondary classroom. We explore how PSTs build understanding across learning opportunities with respect to four modeling competencies: theoretical, task related, teaching and diagnostic. Our findings indicate that PSTs were able to grow across all four competencies. Theoretical competencies developed from time spent working with modeling tasks as learners and working collaboratively with instructors and peers. Task related and teaching competencies took time to develop as PSTs often wrestled with their conceptions of modeling as learners with existing conceptions of teaching and task design. Diagnostic competencies developed from structured time to reflect on lesson enactment and changes that could be made to best support student learning. Overall, we found that PSTs benefit from engaging in modeling tasks as learners and in enacting components of teaching modeling lessons.