# Without testing: when are error terms possibly homoscedastic?

I am facing the following study:

In the 1980's, Tennessee conducted an experiment in which kindergarten students were randomly assigned to regular and small classes, and given standardized tests at the end of the year. (Regular classes contained approximately 24 students and small classes contained approximately 15 students.) Let SC denote a binary variable equal to 1 if the student is assigned to a small class and equal to 0 otherwise. The standard deviation of test scores in the sample is 75. A regression of TS (testscore) on SC yields TS =918 +13.9*CS (5)

R2 = 0.01 ; SER = 74.6

Now I am asking myself: Am I able to conclude that the error term is homo- or heteroscedastic? I would guess that at smaller test levels, they are smaller. And hence not homoscedastic.

• Without testing? How about looking at the plot of the model (residuals)? – user2974951 Dec 17 '18 at 9:11