Plus/minus grading: if given a choice

College Student Journal, June, 2004 by Chip Dixon

After implementation of plus/minus grading, in a series of classes, students were given a choice as to which grading system they individually wanted. Students overwhelmingly chose the straight letter option by a two-to-one ratio. The difference in actual grades earned was minimal, but the preference was clear.

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Several years ago our university, like many others, switched from straight letter grades to a plus/minus grading system. Several professors were initially reluctant about making the change. Our class sizes were relatively small, about 30 students each. With such classes many didn't feel that one could easily go from five possible grades to eleven grade distinctions. In several courses straight letter grading continued to be used.

Eventually a few students asked if they could receive plus/minus grades. In questioning the students' overall desires some classes decided to make the choice optional. Students were asked to decide, before any midterms were given, if they wanted a straight letter grade or if they wanted to use a grading system that included plus/minus grades. This was an individual choice, so students in the same class would be able to select which system they individually preferred.

As one is aware, a plus or minus adds or subtracts three tenths of a grade point. So, for example, while a grade of B is 3.0, a B is 3.3 and a B- is 2.7. While grading approaches can vary tremendously, in the course selected for this study, grading was based on a percentage. To be consistent with adding or subtracting three tenths of a grade point, the course broke up the categories using a similar ratio. Thus, in the plus/minus option, the lower three percentages represented a minus while the upper three percentages were a plus. Using the B grade as an example, in the straight letter option a B ranges from 80 to 89 percent. By contrast, in the plus/minus option the percentages 80 to 82 were a B-, 83 through 86 represented a B, and 87 to 89 resulted in a B . Table 1 shows the comparative grading options.

For six classes, student choices were recorded as were resulting grades. It seems appropriate now to take a closer look at those choices. That is, if given a choice, what do students prefer and how do they perform?

The field is Computing Science. While computing majors may not make the same grading selection as other majors, the course chosen for study was a course mostly populated by those majoring in many fields. The course was "Introduction to Programming". One appreciates that many students avoid computing altogether; one has no control over that. But, a large number of students recognize the importance of being able to indicate a working knowledge of computing. Thus, while "Introduction to Programming" is required of both our majors and minors, the class has significantly more minors than majors. A typical class of thirty students will have about five majors and twenty-five others (minors, those whose major requires this class, and those simply wanting exposure to programming). Introduction to Programming was the most diverse course available for this study.

Starting in 1998 and working forward, six consecutive sections of "Introduction to Programming" were selected for study. Table 2 shows the combined grades of the six classes, broken down by option. Excluded from the results are those who dropped. While drops might show an interesting statistic in their own right, one could not be sure which option those who dropped had chosen. So as not to skew one side or the other, they were removed from the calculations.

Several interesting characteristics can be seen in the results. First is that the plus/minus students had better overall results, with an overall GPA of 2.52 versus 2.29 for the straight letter students. When one looked at the plus/minus students as if they had chosen a straight letter grade the numbers did not drastically change. Had the plus/minus group received straight letter grades their overall GPA would have been 2.49 (Table 3). While the change is minimal, it shows that those who chose the plus/minus option were slightly helped by the choice. That is, more students received a plus than a minus.

A second observation was that slightly more of the plus/minus students failed the class. In the plus/minus group 10 out of 70 failed, representing 14.3%. In the straight letter group 19 out of 154 failed representing 12.3%. The difference between these two is very small; it represents only one additional plus/minus failure. It should be noted that the overall number of participants is less than optimal for more significance in comparisons.

Between the two groups, the big differences were in the number of Bs and Ds earned within each group. In the straight letter group, 43 out of 154 earned a B (27.9%), while 24 out of 154 earned a D (15.6%). With the plus/minus students 28 out of 70 earned a B (40.0%), while only 4 out of 70 earned a D (5.7%). These differences accounted for most of the difference in overall GPA between the two groups. It is pure speculation as to the reasons for these differences. One might argue that those choosing the plus/minus option were indeed more concerned with their grades and thus performed better as a whole; it is surely a possibility.