We use data from two experiments that randomly assign students to groups to show that, so long as ordinal rank has a causal effect on educational achievement, estimates of the effects of peer ability composition obtained from models that omit rank are downward biased. This finding holds both in...

Classroom peers are believed to influence learning by teaching each other, and the efficacy of this teaching likely depends on classroom composition in terms of peers' ability. Unfortunately, little is known about peer-to-peer teaching because it is never observed in field studies. Furthermore,...

This paper investigates the effect of grouping students by prior achievement into different classes (or schools) in settings where students are competing for admission to programs offering only a limited number of places. We first develop a model that identifies the conditions under which the...

A key open question for theories of reference-dependent preferences is what determines the reference point. One candidate is expectations: what people expect could affect how they feel about what actually occurs. In a real-effort experiment, we manipulate the rational expectations of subjects...

While confounding factors typically jeopardize the possibility to use observational data to measure peer effects, field experiments offer the possibility to obtain clean evidence. In this paper we measure the output of four randomly selected groups of individuals who were asked to fill letters...

This paper examines the issue of whether workers learn productive skills from their co-workers, even if those skills are unethical. Specifically, we estimate whether Jose Canseco, one of the best baseball players in the last few decades, affected the performance of his teammates. In his...