When I was a student, I was one of a relative minority who worked in addition to going to classes. That circumstance has changed drastically in the intervening years. According to several recent...

When I was a student, I was one of a relative minority who worked in addition to going to classes.  That circumstance has changed drastically in the intervening years.  According to several recent studies, almost all students work at least part-time, and many work full-time while enrolled in classes (ACE Center for Policy and Analysis, 2006; Alfano and Eduljee, 2013; Perna, 2010).  Both faculty and administrators are concerned that the shift in focus to the world outside of school can affect academic performance.  We compare the GPA of students who work at least part-time outside of class with those who do not work.

What statistical test should be used?