This study models the registration process in order to directly examine the possibility of pre-existing differences between undergraduate students who choose to take service-learning classes compared to those who do not. Foremost among the findings, on most measures there was no significant effect of self-selection. However, students who chose a hypothetical course with a service-learning component reported higher civic responsibility and civic action scores, and reported lower socioeconomic status and greater enjoyment of past service learning than those who chose the hypothetical course without the service-learning component. Challenges and opportunities related to random assignment within service-learning research are discussed.