Here, twenty first-grade teachers were assigned randomly to an experimental “treatment.”
They attended a “month-long workshop in which they studied a research based analysis of
children’s development of problem solving skills in addition and subtraction.” Another twenty
teachers were assigned randomly (they got that right!) to a control group. The students were
then tested for their achievement using a “TBS Level 7” achievement test, and here are the
results: The scores in the test group were 20.95 with a standard deviation of 2.08, and in the
control group were 20.05 with a standard deviation of 1.81. No statistically significant
difference in achievement scores was found, between the two groups.