taged regions, providing pre-primary education, teacher training and mentoring for female students<sup>1</sup> , led to an increase of more than one-third in Grade 4 learning outcomes between 2014 and 2016, enabling these regions to overtake the rest of the country (Asim et al., 2019).

There is substantial evidence that reducing class sizes can lead to improved test scores, although the evidence is mixed and dependent on context and the size of classes before and after reductions. In high-income countries, Angrist and Lavy (1999), exploiting a class size limit of 40 in Israel to conduct regression discontinuity analysis, estimate that reductions in class size can induce substantial improvements in test scores for older primary school students (Grade 4 and 5); however, later analysis using more recent data suggested no impacts on learning from the class size reduction (Angrist et al., 2017). Similarly, Kreuger (1999), analyzing longitudinal data from the United States, finds reductions in class size associated with improvement in standardized tests of at least four percentile points; however, Hoxby (2000), conducting further analysis on similar data, finds no significant impacts on learning from class size reduction. Analyzing cross-country data from 47 countries with pupil fixed effects, Altinok and Kingdon (2011) conclude that the negative effects of class size are small and observed in a minority of countries.

Turning to low- and middle-income countries, where class sizes tend to be significantly larger, Muralidharan and Sundararaman (2013) combine experimental and panel data and estimate that the addition of contract teachers to schools in India to reduce pupil-teacher ratios (PTRs) led to an improvement in student learning of 0.15-0.16 standard deviations (s.d.) in math and language tests. In addition, Duflo et al. (2015) conduct an experimental evaluation of a similar intervention in Kenya found that the apparent benefits of class size reduction only for students in the classes taught by contract teachers and not for students in other classes with regular Government teachers who experienced a similar reduction in class size, concluding that improved practices and reduced absenteeism by contract teachers compared to Government teachers was the reason for gains in learning rather than class size reduction.

In recent years, new research has directly explored the question of how large class sizes must be to negatively affect learning outcomes. Datta and Kingdon (2021), examining large-scale test data from India with pupil fixed effects, find that negative effects from large class sizes begin at a size of approximately 40 for science subjects and 50 for non-science subjects, and that India could allow its current national PTR to increase to 40<sup>2</sup> without negatively affecting test scores.

However, there is a lack of rigorous analysis of the effects of class size reduction focused on countries where class sizes are substantially larger. Evidence from Malawi suggests that PTRs above 90 are associated with significantly lower test scores in Grade 4, equivalent to several weeks’ lost learning, even when controlling for a wide range of school, teacher and student characteristics (Asim and

> 1 The Education Quality Improvement Programme (EQUIP-Tanzania)

> 2 From a current 22.8

3