This research compares a student-centered, proficiency-based assessment and reassessment of learning outcomes (PARLO) system to traditional assessment in a college-level introductory statistics class. The PARLO class was assessed on learning outcomes using a three-tiered proficiency scale and given the opportunity to resubmit assignments to increase their rating. Students' attitudes towards statistics improved more in the PARLO group, but no differences between groups were found on the CAOS test or on a common final exam. Within the PARLO group, students with a higher resubmission rate scored better on the final exam and those who resubmitted and achieved proficiency performed similarly to those achieving proficiency with the first submission. Assessing proficiency on specific learning outcomes allowed both students and the instructor to better evaluate learning. (Contains 2 tables and 3 figures.)