Mari Rege and Odny Solheim are still in denial.
Where before they were claiming that we were using transitory and unpredictible variation in our study to estimate class size effects, this is now off the table.
Now it is something else:
Schools are facing large and unpredictible changes in class sizes from cohort to cohort, and on top of it schools are unable to handle that.
Rege and Solheim forget to mention that these are conjectures.
They also forget to check the data.
If we do that for the period we study (1978-2003), we see that for the large majority of schools class size in our data varies by at most 5 pupils from cohort to cohort.
For a given school these changes are on average zero across cohorts.
Schools therefore have typical class sizes with small variations around the mean.
These changes are predictible (in our data with past changes in enrollment) and are small.
And not unpredictible and large as claimed by Rege and Solheim.