Contribution: Our work focuses on building research capacity in engineering education research (EER). We operationalize enculturation of novice researchers into the EER community by studying temporal changes in the social networks of engineering faculty participating in a mentorship-based training grant. Background: The U.S. National Science Foundation's Research Initiation in Engineering Formation (RIEF) is a training grant for engineering faculty without prior EER experience who seek to conduct EER. Faculty mentees work with an experienced social science researcher during a funded two-year project. During this time, mentees must undergo a paradigm shift from engineering research to social science, which includes building research skills and becoming enculturated into the EER community. Research Questions: What are the characteristics of RIEF mentees' professional networks for EER? How do RIEF mentees' networks change over time, as operationalized by professional interactions, communication about the RIEF project, and collaborations? Methodology: We use social network analysis to investigate the development of EER professional networks of RIEF mentees and their interactions with other community members during the first year of their research initiation training. Findings: Overall, mentees' professional networks for EER increased (i.e., reported more connections) after one year. However, when mentors had limited prior connections to the EER community, their mentees' social networks for EER are isolated compared to mentees whose mentors have a higher number of connections to community members. Our findings have implications for mentored training programs, suggesting that well-connected mentors are best placed to enculturate mentees into a research community.