This issue of the Adult Skills in Focus series looks at gender differences in reading (literacy) and mathematics (numeracy) skills, and in particular how these differences evolve as people grow up. The analysis use data on three different assessments, administered to children in fourth grade (around 10 year-olds), to 15-year old adolescents, and to young adults aged 26-27. The data shows that girls have a small advantage in literacy at age 10, which grows larger by age 15. However, at age 26 this advantage disappears, and young adults achieve on average the same scores in the literacy assessment. The picture is very different in the case of numeracy skills. At age 10 the gaps are very small, with a tiny advantage for boys. The gap is larger at age 15 and grows even more by age 26, when young men achieve on average much higher scores. A possible explanation for these results is that men specialise in occupations and fields of study that make higher use of numeracy skills; men are also able to close the gap in literacy skills because reading is a transversal skill that people need to master to be successful in a wider range of occupations.