Bridging the theory-practice gap remains a challenge in preparing preservice elementary teachers for science teaching. Research experiences for undergraduates (REU) offer a potential way to help preservice elementary teachers (PSTs) come to value and implement research-based science teaching. REUs come in many forms but often take the form of either extracurricular research with a practicing scientist. Alternatively, practitioner inquiries are often used as part of a teacher preparation course or practicum but often are limited in time and scope. In this study, we report on a novel approach to an REU that combined the features of a traditional REU and practitioner inquiry, which we refer to as Extracurricular Practitioner Inquiry (EPI). PSTs collaboratively developed, tested, and prepared curricular units for publication as part of an extracurricular, funded project. A mixed-methods approach, including nonrandom matched pairs and semi-structured interviews, was used to investigate the impact of the EPI experience on PSTs' knowledge and beliefs about science teaching. As a result of their participation in the novel EPI, when compared with a control group, the PST participants developed beliefs more consistent with research-based science teaching. Support from collaborators, shifts in self-perception, and improved understanding of the research-practice relationship seem to have mediated changes in the PSTs' knowledge and beliefs about science teaching.