This is the final paper in a five-paper series describing our national study of the teaching and learning of cosmology in general education astronomy college-level courses. A significant portion of this work was dedicated to the development of five new Lecture-Tutorials that focus on addressing the conceptual and reasoning difficulties that our research shows students have with frequently taught cosmology topics, such as the expansion of the universe, the Big Bang, and dark matter. We conducted a systematic investigation of the implementation of these new Lecture-Tutorials and resulting learning gains in order to test the efficacy of these new Lecture-Tutorials. Our investigation included classroom observations, results from pre–post testing using four conceptual cosmology surveys, and comparisons between classes in terms of the class time spent on cosmology topics and other instructional strategies used to teach cosmology. We used this combination of qualitative and quantitative research results to evaluate the conceptual understandings of students who used the new cosmology Lecture-Tutorials compared to those students who did not. The analysis of our data shows that, in many cases, classrooms that used the cosmology Lecture-Tutorials saw a greater increase in their students’ conceptual cosmology knowledge compared to classrooms that did not use the cosmology Lecture-Tutorials. However, our results also indicate how instructors implement the Lecture-Tutorials into their classrooms strongly influences their students’ learning gains.