Repair Kit Fix 11: Calculating Final Grades

Fix 11: Don’t rely on the mean; consider other measures of central tendency and use professional judgement.

“Grades may mislead when they are based simply on calculating the mean(average) of a series of scores, due to the effect of outlier scores.  The fix for grades broken in this way in not use the mean as ‘the measure’ by considering other means of central tendency…it is truly ‘mean’ to students because it overemphasizes outlier scores, which are most often low outliers.”

This one gets me, I assume  this is calculating grades using only summative assessment scores.  The example shows only 10 scores so I would assume summative because if you counted formative assessment/homework there would be many more scores.  However the example is effective in showing how one low outlier score can make a big difference in a final grade if you go by mean.  This is most definitely a time where using median or mode would be a more accurate representation of achievement.

“If students are very consistent each measure (mean, median, mode) will get the same results and mean will suffice.  But the more inconsistent a student’s performance is the less effective anh of the measures is in accurately summarizing student achievement.” (page 91)

This is a really good point but it leaves me wondering how you do calculate a grade of a student with inconsistent performance.

“The median or the mode are generally more appropriate than the mean when confronted with extreme scores” (page 91)

Like top and bottom scores being dropped in judged sports like gymnastics or ice skating.  Maybe you can do that kind of thing for each standard while being sure to look for reasons for extreme scores especially the low ones.

“As teachers we must ask the question ‘Based on all the evidence of achievement a student has produced, which summary symbol most accurately represents the achievement.”

This allows teachers some flexibility in determining of grades and while I like that I worry about the reaction this might bring.  I also wonder how this will work considering so many schools/districts use computer grade books that calculate mean as the automatic method.  Maybe the teacher could exempt those outlying scores or find out if there’s another way to calculate grades in the system.  Perhaps districts/schools applying the fixes will look into different online grading programs, programs that allow teachers more flexibility in grading.

Teacher Vignette: In this case the teachers overrode grades when the mean was not the most accurate measure.  It was comforting to know that they had to do this for very few students though.




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