An instrumental variables (IV) identification strategy that exploits statutory class size caps shows significant achievement gains in smaller classes in Italian primary schools. Gains from small classes are driven mainly by schools in Southern Italy, suggesting a substantial return to class size...

The matching method for treatment evaluation does not balance selective unobserved differences between treated and non-treated. We derive a simple correction term if there is an instrument that shifts the treatment probability to zero in specific cases. Policies with eligibility restrictions,...