Boggild‐Jones, and Gardiner 2017). Ideally, a separate initiative would collect cost data following a standard set of guidelines such as those laid out in Dhaliwal et al. (2013).

This review finds that general interventions are often comparable in impact to girl‐targeted interventions in improving access to school and learning once at school. But if a policy maker’s primary concern is improving girls’ education, then perhaps investing in girl‐targeted interventions would allow similar gains at much lower cost – i.e., just paying for the girls rather than girls and boys. This argument plays out differently for access versus learning interventions. For access interventions such as cash transfers, the cost could indeed be potentially reduced by targeting only girls. Indeed, several of the most effective general interventions were cash transfer programs that happened to not target girls specifically. One could imagine replacing those programs with girl‐only cash transfer programs and potentially achieving similar gains. For learning interventions, such as structured pedagogy interventions, many are introduced at the level of the school, so that in mixed‐gender schools, there is no clear cost gain to trying to limit the impact to girls only.

# Program attributes

We gathered data on a number of program attributes with the aim to provide more information on the most effective programs. For example, the average program size of the most effective access interventions is 262 students and for learning interventions, is 556 students. With the exception of the cash transfer programs, all others among the ten most and least effective programs are pilot programs. This is a result of the fact that most interventions that are carefully evaluated tend to be pilots. Therefore, we cannot from this sample infer whether or not pilot programs are more effective than those that have been implemented at scale. Another attribute that we examined was the level of education that the top programs targeted. In terms of access interventions, 7 of the top 10 interventions targeted school‐aged children in general, often between age 6 up to age 16 – working through the household rather than the school, trying to get out‐of‐school children into school. For learning interventions, 9 in 10 focused on the primary level, and half of them were designed to improve learning in grades 1‐3. There is great interest in programs for adolescent girls, but many of those programs focus on building life skills and increasing earning capacity directly (see, for example, (Adoho et al. 2014; Bandiera et al. 2018; Bandiera et al. 2019) rather than keeping girls in school and increasing their learning ability. In many low‐ and middle‐income countries, children and youth can still significantly improve their literacy and numeracy all through primary and secondary school (Evans and Yuan 2019), and so there will be great value in continuing to evaluate programs and increase learning and access for adolescents. We also examined if authors included any gender component in their interventions. We found that besides girl‐targeted programs, only 1 general intervention in the top 20 had a girl‐friendly component, which was to provide gender‐differentiated school subsidies (Barrera‐ Osorio et al. 2017).

# What has been studied

A key limitation of this work is that it only surveys those interventions that have been evaluated. One can imagine a wide array of girl‐targeted interventions that could still be tried or that have 14