This paper is the first to use the individual level, longitudinal catch-up growth of boys and girls in a historical population to measure their relative deprivation. The data is drawn from two government schools, the Marcella Street Home (MSH) in Boston, MA (1889–1898), and the Ashford School of the West London School District (1908–1917). The paper provides an extensive discussion of the two schools including the characteristics of the children, their representativeness, selection bias and the conditions in each school. It also provides a methodological introduction to measuring children’s longitudinal catch-up growth. After analysing the catch-up growth of boys and girls in the schools, it finds that there were no substantial differences between the catch-up growth by gender. Thus, these data suggest that there were not major health disparities between boys and girls in late-nineteenth-century America and early-twentieth-century Britain.