Post-Randomization Peer Compositional Stability
RCTClinical Trial
Post-assignment student mobility and the entry of non-sample peers into study classrooms can alter peer composition, potentially confounding treatment effect estimates if high-effectiveness teachers systematically receive better non-sample peers.
Picture this
If participants in a fitness study invite outside friends to join their workouts, researchers must verify that the incoming friends do not give certain workout groups an artificial boost compared to others.
What the evidence says
Assigned teacher effectiveness showed no statistically significant relationship with peer baseline math scores (coefficient = 0.246, SE = 0.164) or other peer traits; joint hypothesis p-values were 0.405 for grades 4–8 and 0.321 for high school, proving post-randomization peer stability.
- Who was studied
- N = 27,255 randomized students in grades 4–8 across 619 randomization blocks in 6 urban school districts.
- How
- SURE joint hypothesis regression of actual spring classroom peer characteristics (baseline math/ELA scores, special education %, ELL %, race, absences, suspensions) on assigned teacher effectiveness.
What to do
Assess the baseline characteristics of actual end-of-year classroom peers and regress them on assigned treatment intensity to rule out peer compositional contamination.
From the source
"In sum, despite the movement into and out of the randomized classrooms, the peers to whom randomized students were exposed were not systematically different based on the effectiveness of their randomly assigned teacher."
Have We Identified Effective Teachers? Validating Measures of Effective Teaching Using Random Assignment