Our study was based on exploring CS1 students' implicit theories of intelligence. Referencing Dweck and Leggett's  framework for implicit theories of intelligence, we investigated (1) how students' implicit theories changed over the course of a semester, (2) how these changes differed as a function of course enrollment and students' self-regulation profiles, and (3) whether or not implicit theories predicted standardized course grades and performance on a computational thinking knowledge test. For all students, there were significant increases in entity theory (fixed mindset) and significant decreases in incremental theory (growth mindset) across the semester. However, results showed that students had higher scores for incremental than entity theory of intelligence at both the beginning and end of the semester. Furthermore, both incremental and entity theory, but not semester change in intelligence theory, differed based on students' self-regulation profiles. Also, semester change in entity theory differed across courses. Finally, students' achievement outcomes were weakly predicted by their implicit theories of intelligence. Implications for student motivation and retention in CS and other STEM courses are also discussed.