This article illustrates the value of large-scale impact evaluations with counterfactual components. It begins by exploring the limitations of small-scale impact studies, which do not allow reliable inference to a wider population or which do not use valid comparison groups. The paper then describes the design features of a recent large-scale…

This study explores the differential effect of two types of corrective feedback strategies--explicit and implicit--on the acquisition and retention of correct past form of irregular verbs by Iranian English as Foreign Language (EFL) learners. Sixty out of 80 pre-intermediate EFL learners were selected as the participants, based on their…

Can providing learner support materials, particularly custom-designed workbooks, improve primary mathematics achievement more cost effectively than providing conventional textbooks? To contribute to this debate, this paper reports on the findings of a study conducted in 2010 by a consortium of educational researchers at JET Education Services and…