India is home to the world’s largest population of illiterates. And part of the blame, according to a new study, may lie in the country’s preference for sons over daughters.

Despite education being offered as a fundamental right, more than 40% of India’s children drop out of elementary school—and the country has more than 287 million illiterates, 37% of the global total. Moreover, 40% children are stunted in India, which means they don’t grow to their full potential because they don’t get the necessary resources.

Part of the blame lies in the cultural preference towards the male sex, according to Adriana Kugler of Georgetown University and Santosh Kumar of Sam Houston State University who authored the working paper, published by the American non-profit, National Bureau of Economic Research.

They come to these conclusions by analysing district-level household survey from 2007-08 to examine the impact on educational outcomes and the national family health survey from 2005-06 to examine the impact of family size on weight and height of young children. Both these surveys are among the most comprehensive surveys produced in the country.

One way in which this bias manifests is in families where, when the first born is a girl, parents will continue to have more children until they have a boy. Thus, in a society that prefers sons, the first child’s sex in India becomes an indicator whether or not a second child will be planned, and of the total number of children in the household. This, in turn, decides the size of the family.

This situation does not have much effect on children’s literacy or health in a rich family. There these “extra” children tend to receive at least the minimum amount of resources needed to survive and thrive. In lower caste, rural and poor households, however, the limited resources means that an extra child takes away some resources from all the children in the family.

An extra child in the family reduces schooling, on average, by 0.1 years. Furthermore, that extra child reduces the probability of ever attending or being enrolled in school by up to 2%. Both numbers may seem small, but for the size of India’s young population, the upshot is that millions don’t go to school enough or at all.

However, the impact of an extra child “in terms of reducing enrolment and attendance double and the impact of an extra child on years of schooling increase fourfold for illiterate and poor mothers, suggesting much larger gains from reducing family size in disadvantaged households,” according to the report.

Kugler and Kumar also looked at the effect on the health of children as families became larger. But they got mixed results on the impact it had had. However, Quartz recently reported that another study by Northwestern University’s Seema Jayachandran and Harvard University’s Rohini Pande had clearly shown negative results.

The Indian first and eldest son tends to be taller than an African firstborn. If the eldest child of the family is a girl, and a son is born next, the son will still be taller in India than Africa. For girls, however, the India-Africa height deficit is large. It is the largest for daughters with no older brothers, probably because repeated attempts to have a son takes a beating on the growth of the girls.

As is the case with any working paper, there is a chance that Kugler and Kumar’s finding may not withstand stronger scrutiny. However, Kugler remains confident. “We have done many robustness checks so the results are unlikely to change,” she told Quartz.