Summer of code programs connect students to open source software (OSS) projects, typically during the summer break from school. Analyzing consolidated summer of code programs can reveal how college students, who these programs usually target, can be motivated to participate in OSS, and what onboarding strategies OSS communities adopt to receive these students. In this paper, we study the well-established Google Summer of Code (GSoC) and devise an integrated engagement theory grounded in multiple data sources to explain motivation and onboarding in this context. Our analysis shows that OSS communities employ several strategies for planning and executing student participation, socially integrating the students, and rewarding student’s contributions and achievements. Students are motivated by a blend of rewards, which are moderated by external factors. We presented these rewards and the motivation theory to students who had never participated in a summer of code program and collected their shift in motivation after learning about the theory. New students can benefit from the former students' experiences detailed in our results, and OSS stakeholders can leverage both the insight into students’ motivations for joining such programs as well as the onboarding strategies we identify to devise actions to attract and retain newcomers.

Open Source Software (OSS) communities depend on continu-ally recruiting new contributors. Some communities promote initiatives such as Summers of Code to foster contribution, but little is known about how successful these initiatives are. As a case study, we chose Google Summer of Code (GSoC), which is a three-month internship promoting software development by students in several OSS projects. We quantitatively inves-tigated different aspects of students' contribution, including number of commits, code churn, and contribution date inter-vals. We found that 82% of the studied OSS projects merged at least one commit in codebase. When only newcomers are considered, ~54% of OSS projects merged at least one com-mit. We also found that ~23% of newcomers contributed to GSoC projects before knowing they would be accepted. Addi-tionally, we found that the amount of commits and code of students with experience in the GSoC projects are strongly correlated with how much code they produced and how long they remained during and after GSoC. OSS communities can take advantage of our results to balance the trade-offs in-volved in entering CCEs, to set the communities' expectations about how much contribution they can expect to achieve, and for how long students will probably engage.