Research shows that interaction with female STEM mentors plays an important role in helping girls develop a positive STEM identity that supports interest and persistence within STEM. The Imagine Your STEM Future Program does just that by pairing female engineers from Raytheon and University of Arizona students with high school girls at Desert View High School. Mentors commit to participate in the program for an entire school year, providing the opportunity to build sustained, robust relationships with girls. The Imagine Your STEM Future program is integrated into the school day in order to increase accessibility for student participants and takes place 3-4 days per week. The curriculum includes a combination of hands-on STEM activities, reflective group conversations on STEM academic and career pathways, the importance of diversity in science and engineering communities, and visits from inspiring STEM role models. Through implementing the engineering design process, girls begin to build STEM skills such as designing, building, and prototyping, but more importantly for this program, learn communication and collaboration skills as they work in small groups. Each element of the program has been chosen based on best practices for maximizing impact on girls’ interest and persistence in STEM.