Girls outperform boys in reading; boys outperform girls in mathematics all across the developed world.

Indeed, the Organisation for Economic Co-operation and Development's (OECD) Programme for International Student Assessment (PISA) study reveals that, at 15 years old, girls do better in reading in all countries, while boys do better in mathematics in six out of 10 countries. These gender gaps are observed as early as the first year of school in reading, and tend to appear more progressively in mathematics after children have started school.

They also vary with economic status. The gap favouring girls in reading tends to be larger in poorer countries and among low-socio-economic-status (SES) children within countries. In contrast, the gap favouring boys in mathematics appears larger in richer countries and among high SES children within countries.

Recently, there appears to be a consensus among researchers that aptitude (in any domain) is not gendered. So what creates those gender gaps and how do we close them?

In my recent research with Deborah Cobb-Clark, from the University of Sydney, we interrogated the source of the gender gap using data on third-grade numeracy and reading in Australia.

Exploiting data from the Longitudinal Survey of Australian Children, in which information on child development reported by parents and teachers is linked to each child's NAPLAN results, we evaluated the contribution of a large number of individual, family and school factors to these gender gaps.

In particular, information on parents' expectations for and investments in their children, as well as each child's school readiness, allowed us to distinguish between gender gaps that exist before children start school from those that emerge after.

Consistent with international evidence, Australian girls in low and middle-SES families score better in reading, while boys in high-SES families score better in numeracy.

This supports the notion that skill advantages are not naturally gendered but are the result of complex human capital formation processes. And what creates these differences varies between boys and girls.

For example, girls' advantage in reading originates even before starting school. They score better on school readiness tests at four years old, and have better teacher-assessed literacy skills than boys in kindergarten.

In contrast, boys' advantage in numeracy develops later and appears more complex. Before school, high-SES boys do not have more of the characteristics that are associated with higher numeracy test scores than their female peers. For example, they are less ready for school than girls at four years-old and score the same as girls on a cognitive development test at six years-old. In essence, boys are able to produce better outputs with lower inputs.

Overall, the complex pattern of gender gaps across subject areas and family circumstances makes it unlikely that a single overarching process drives the relationship between gender and educational achievement. As a result, different approaches are needed to address gaps in numeracy and in reading.

While gendered educational practices are unlikely to be the main driver of gender gaps in reading (which exist before school), they could contribute to gender gaps in numeracy. For instance, the advantage of high-SES boys in numeracy partly arises because they benefit more than high-SES girls from attending pre-school.

sensible policy responses

Also, while the numeracy performance of high-SES boys is unaffected by school type, our research suggests that (all else being equal) high-SES girls attending Catholic schools have lower achievement in numeracy compared to high-SES girls attending government schools. Ensuring that educational practices do not favour one gender over the other could support girls' achievement in numeracy.

In contrast, potential avenues for reducing gender gaps in reading may lie in the home. For example, reading to boys more often, engaging with them about reading and showing them it is not a girl-only activity could help boys develop a taste for reading.

Identifying sensible policy responses to address gender gaps in early achievement are particularly important because the cumulative nature of the learning process has the potential to compound any gaps in achievement over time.

In particular the disadvantages faced by boys seem to have been overlooked by policy makers although they started lagging behind girls in educational attainment more than 50 years ago. This is especially worrying given that boys' underachievement could pose serious threats to economic growth and social wellbeing in the future if it leads to higher drop-out rates, more mental health issues, more criminality or more unemployment. Of course, girls' disadvantage in numeracy also needs to be addressed as it feeds into inequalities observed later on, such as investments in STEM (science, technology, engineering and mathematics) subjects, wages and glass ceiling effects.

However, there is still much to be done in order to uncover which mechanisms underlying the gender gaps are relatively more important and under which circumstances. For instance, how much of these gaps are due to the types of activities parents do with their children (reading, cultural, sport) and the transmission of gender stereotypes? Research to scientifically test these alternative hypotheses would be particularly valuable in identifying sensible policy responses.

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