This paper presents a summary of action research investigating statistics students' understandings of the sampling distribution of the mean. With four sections of an introductory Statistics in Education course (n=98 students), a computer simulation activity (R. delMas, J. Garfield, and B. Chance, 1999) was implemented and evaluated to show students the sampling distribution "in action," as recommended by many authors and statistics professors. Assessments after the activity point to clear deficiencies in student understanding, such as not understanding how sample size affects the shape and variability of sampling distributions. With the addition of the computer simulation, the understandings of many students are still incomplete. This was most evident as the instructor moved forward in class to introduce inferential statistics. The paper discusses some of the deficiencies noted in student understandings and how the action research cycle will continue to work on these deficiencies. The posttest is attached. (SLD)