EducationHuman capitalPositive

Tennessee STAR — Student/Teacher Achievement Ratio

Tennessee Department of Education / SBER / Vanderbilt / Harvard · Tennessee, USA · 1985

Summary

The Tennessee STAR experiment is the most influential randomized trial in the history of American education policy. Its finding — that students in small classes outperformed those in regular classes by 4–8 percentile points, with effects especially large for low-income and minority students — was replicated across 79 schools and remained detectable through middle school even after students returned to regular-sized classes. The Chetty et al. follow-up 25 years later found the effects on adult earnings, college attendance, and home ownership, making STAR one of the few educational interventions with documented adult-life returns. The experiment's policy impact was immediate and massive: California spent $1.5B reducing class sizes in 1996. The limitation that haunts the STAR results is the transition problem: scaling class-size reduction requires hiring more teachers, which can reduce average teacher quality if the supply of effective teachers is inelastic. STAR answers 'does class size matter?' with a clear yes; it cannot answer 'what happens when you reduce class sizes everywhere?'

Research question

"Does reducing class size in the early grades (K–3) improve academic achievement, and do any benefits persist beyond the years of small class attendance?"

Methodology

Intervention

11,600 students entering kindergarten were randomly assigned to one of three conditions: small class (13–17 students), regular class (22–26 students), or regular class with a full-time teacher's aide. Teachers were also randomly assigned to classes. The experiment ran through 3rd grade. Students then returned to regular-sized classes in 4th grade, and long-term follow-up tracked outcomes through college.

Assignment

Randomized controlled trial; within-school randomization of students and teachers to class type; 79 schools across Tennessee, stratified by location (inner-city, urban, suburban, rural); Krueger (1999) is the definitive econometric analysis of the data

Sample size

11,600 students in Kindergarten through 3rd grade across 79 Tennessee schools

Primary outcome

Standardized test scores in reading and math (grades K–8); graduation rates; college attendance; earnings in adulthood

Effect estimate

Test scores: small-class students scored 4–8 percentile points higher than regular-class students; effects largest for minority students (+10 pp) and low-income students (+8 pp). Persistence: test score advantage visible through 8th grade (4–5 years after returning to regular classes). Long-term: Chetty et al. (2011) found STAR students had 1.6% higher earnings in adulthood; college attendance rates 2.7 pp higher; probability of home ownership 4.6 pp higher.

Decision

Results directly triggered California's class-size reduction initiative (1996), reducing K–3 class sizes to 20 in all public schools; Wisconsin and Indiana launched similar reductions; STAR findings became a central exhibit in US education policy debates for 30 years; Chetty et al. long-run analysis (2011) strengthened the policy case by showing the effects on lifetime earnings; international replications (UK, Denmark) showed smaller effects, raising questions about scaling from a single-state experiment; economists continue to debate effect size vs. cost of implementation

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Result

Positive

Evidence strength

Strong

Randomized controlled trial with large sample.

Replication status

Partially replicated

Institution

Tennessee Department of Education / SBER / Vanderbilt / Harvard

Location

Tennessee, USA

Year

1985

Policy area

Education

Mechanism

Human capital