This study describes the design and implementation of a science outreach program (elementary; 2nd-5th) and its associated student outcomes. Key features of the program include: (a) phenomenon-based, NGSS-aligned curriculum designed by science education experts and influenced by educational, sociocultural, and cognitive science theories, (b) active engagement by elementary students in experimentation and exploration of a common phenomenon (2 per year, called modules) across multiple sessions (6-8 per module), (c) professional development (PD) provided to scientists (mentors) and teachers to supply classrooms with multiple (5-7) adult more knowledgeable others (AMKOs), and (d) close classroom interaction between elementary students and mentors, allowing for students to participate in evidence-based sense-making through whole-class and small-group discussions. We examined the effects of program participation on students' epistemological understanding of science (EUS) and attitudes toward science, as well as surveyed teachers to determine how they felt the program affected students' attitudes and EUS. Student measures indicated they developed a deeper understanding of the process of scientific knowledge generation and were more likely to report liking science more than less. Similarly, teachers' self-reports corroborated these results, as well as showed teachers thought the structure of the program effectively integrated mathematics and language arts.