As undergraduate institutions rely more heavily on teaching assistants (TAs) they are simultaneously encouraging implementation of course-based research experiences (CBREs). Due to the dynamic nature of CBREs, it is challenging to assign novice TAs to instruct these types of classes. A 10-week CBRE was designed to guide both TAs and their students through a tiered mentored course. The CBRE scaffolded the learning experience for both the TAs and their students for the first 4 weeks with preset labs and then allowed 6 weeks for the TAs to guide their students through asking a scientific research question, designing an experiment, and implementing their research design. This course utilized the researchers as TA instructors, undergraduate students as TAs and research mentors, and high school students as mentees of the undergraduate students. This qualitative study describes the course objectives and design as well as the self-reported science content, teaching, and mentoring gains of the CBRE TAs. These findings support that TAs being trained as research mentors may increase learning gains in both the mentor and mentee populations.