Scientific modeling and coding are critical skills for K-12 students. Teaching scientific modeling entails supporting K-12 students in constructing, manipulating, and developing their own models to advance knowledge of a complex system or phenomenon. Learning to code prepares students to solve problems using computational concepts and processes. This dissertation research begins the pathway toward supporting students in using block-based coding to externalize and develop their models through the process of creating simulations of science phenomena. Research indicates that teachers need professional learning on scientific modeling and teaching with coding. An instructional module and online tool named Coding in Scientific Modeling Lessons (CS-ModeL) were designed to support preservice science teachers learning to code and to integrate block-based coding into scientific modeling lessons. CS-ModeL was designed and developed based on proposed design guidelines that emerged from review of relevant literature (Chapter 2). A qualitative pilot study was conducted to implement CS-ModeL in a methods of science teaching course (Chapter 3). Results indicated that study participants developed more refined models of science phenomena and perceived coding as a key skill for K-12 education but failed to design lessons in which block-based coding supports scientific modeling. Results informed recommendations for CS-ModeL redesign. A mixed methods study was conducted to implement the redesigned CS-ModeL (Chapter 4). The study investigated if and how preservice teachers epistemological understanding of models and modeling as well as their understanding of computer science concepts changed after participation in CS-ModeL. The study also examined how participants used coding in scientific modeling lessons. Results showed that most participants developed a more sophisticated epistemological understanding of models and modeling, as well as an understanding of computer science concepts. Results also indicated that participants designed lessons wherein block-based coding was used to support scientific modeling either as an exploration tool or as a research tool. Additionally, lessons focused on computer science practices rather than specific concepts. It was noteworthy that there were inconsistencies between participants epistemological understanding of models and modeling and their lesson design. Conclusions and directions for future research are discussed.