Open Source Software (OSS) communities depend on continually 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 investigated different aspects of students' contribution, including number of commits, code churn, and contribution date intervals. 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 commit. We also found that ∼23% of newcomers contributed to GSoC projects before knowing they would be accepted. Additionally, 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 involved 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.