Don’t Think Class Size Affects Achievement? Think Again.
It is already obvious that class sizes are up this year — which will give School Year 2011-12 the dubious honor of being the fourth straight year of class size increases. The DOE won’t have official numbers until November, but budget cuts resulted in the loss of some 2,500 teachers this year, enrollments are rising and now we have theDay 6 class size grievance counts: nearly 7,000, up from 4,370 this time four years ago.
Will the bigger classes affect achievement? Results from just a single year suggest they will. The UFT Research Dept. looked at fourth grade, where class sizes rose an average of about one-half a child (0.47) last year. Then we divided the fourth grade into schools where class size rose more than the average, and schools where it rose less, and looked at their achievement in math. The difference was pronounced. While the majority of schools improved in math last year, schools where 4th grade class sizes rose by less than the average improved two percentage points more than schools that had larger-than-average class size increases.
| School year 2010 to 2011 | Growth in class size | Change in math proficiency |
|---|---|---|
| Grade 4 (274 schools) | Less than 0.47 student | +5.2 points |
| Grade 4 (426 schools) | More than 0.47 student | +3.2 points |
Another way to parse the same information is by dividing the group into quartiles (quarters). When we did this we
