Comparing the Percentile Rank of the Average Student in One Cohort to the Percentile Rank of the Average Student in a Later Cohort

Parents of students in Valley View Elementary were concerned that the achievement of students had declined over the last few years. From looking at past communications they saw that in 2012 the average fifth grader scored at the 58th percentile rank on a nationally normed test. But in 2014 the average fifth grader scored at the 54th percentile rank. Was this decline large enough to be considered educationally significant? There were 85 students in the fifth grade each year. 

The parents entered this information into the EIC and got the results shown below.  The effect size is -.10, below the level typically seen as educationally significant, and the probability level of .51 indicates that the result was likely to have occurred by chance. Based on these results one could suggest that the parents need not be overly worried at this point about declining achievement, although they certainly would be advised to continue to monitor the students’ achievement.