Open-source software (OSS) often evolves from volunteer contributions, so OSS development teams must cooperate with their communities to attract new developers. However, in view of the myriad ways that developers interact over platforms for OSS development, observers of these communities may have trouble discerning, and thus learning from, the successful patterns of developer-to-team interactions that lead to eventual team acceptance. In this work, we study project communities on GitHub to discover which forms of software contribution characterize developers who begin as development team outsiders and eventually join the team, in contrast to developers who remain team outsiders. From this, we identify and compare the forms of contribution, such as pull requests and several forms of discussion comments, that influence whether new developers join OSS teams, and we discuss the implications that these behavioral patterns have for the focus of designers and educators.