—Open source software systems rely on community source code contributions to fix bugs and develop new features. Unfortunately, it is often difficult to become an effective contributor on open-source projects due to the complexity of the tools required to develop and test new patches and the challenge of breaking into an already-formed social organization. To help new contributors learn their development practices, OSS projects have created onboarding programs that, for example, identify easy ‘first bugs’ and mentor new developers’ contributions. However, we found that developers who join an organization through these programs are half as likely to transition into longterm community members than developers who do not use these programs. Measuring the impact of these programs is important, as coordinating and staffing onboarding projects is expensive. This paper examines onboarding programs employed by Mozilla and demonstrates that they are not as effective at transitioning n...