While there is a focus internationally on measuring literacy and numeracy skills at age 15, as captured in the OECD Programme for International Student Assessment (PISA), at least two aspects are neglected in debates on learning achievement.

First, literacy and numeracy skills continue to develop in some populations after the end of compulsory schooling. For example, as data from the OECD Adult Literacy and Lifeskills Survey show, these skills reach a peak in the early 30s before they start to decline. This means that young people develop cognitively for many years after finishing compulsory education, at least if they benefit from post-secondary education opportunities.

Older adults possess a lower level of literacy and numeracy skills, mainly because people lose skills as they age but also partly because the quality of education in some countries has improved, which works for the benefit of younger adults.

Those with less education not only have lower skills as they enter adulthood but are also more likely to find employment in occupations that do not require the use and development of their skills. They are also less likely to benefit from adult education opportunities.

Second, literacy and numeracy skills do not develop in the same way for all populations. A recent analysis of data from PISA surveys on students at age 15 and Programme for the International Assessment of Adult Competencies (PIAAC) surveys of the same cohort 12 years later, brought up interesting conclusions about how young people’s skills develop and what factors influence their development.

Since 2000, PISA surveys have been telling us that two factors make you more likely to have a lower literacy score: being a boy and coming from a lower socioeconomic background. Whether or not an individual is from a low socioeconomic background has been linked to such easy-to-observe factors as the number of books at home or the parents’ level of education.

Socioeconomic disparities widen in young adulthood

We have long known that young adults whose parents have less education have far lower literacy levels than those whose parents were educated at the post-secondary level. The OECD research shows us that the gap between those with educated parents and those without increases over time: by 20% from the age of 15 to the age of 27.

In some countries, such as Ireland, New Zealand, and Norway, the gap more than doubled. The data also suggest that the growth in disparities is concentrated amongst the lower performers at age 15. This could be because more disadvantaged young people are less likely to enter further education or to enter into occupations that ask them to apply and develop their skills.

Boys’ skills seem to catch up with girls’ – if a gap ever existed

But the analysis also shows that the large literacy gaps that existed between boys and girls at age 15 are all but gone by age 27, with low-performing males making the biggest leaps in performance.

Almost all assessments of literacy skills at school suggest that girls do better in reading, a fact reiterated in the 2018 Gender Review. But was there such a gap in the first place?

Unlike PISA and other school-based assessments of reading skills, the PIAAC survey suggests that, even at age 16, the gender disparity in literacy skills was already very low.

One question therefore is whether the different ways in which tests are administered matters. The PIAAC test takes less time to complete, uses technology, and involves a trained interviewer visiting the household. All these factors could help boys be more engaged and focused, compared to the school-based PISA assessment, where peer pressure effects may lower the extent of boys’ engagement.

Learning assessments are critical for understanding education systems and the distribution of skills in the population. But they also depend on context and require us to be alert on how to interpret their findings.