Reliability of the g factor over time in Italian INVALSI data (2010-2022): What can achievement-g tell us about the Flynn effect?

Generational intelligence test score gains over large parts of the 20th century have been observed to be negatively associated with psychometric g. Recent reports about changes in the cross-temporal IQ trajectory suggest that ability differentiation may be responsible for both changes in g as well as increasingly (sub-)domain-specific and inconsistent trajectories. Schooling is considered to be a main candidate cause for the Flynn effect, which suggests that school achievement might be expected to show similar cross-temporal developments. In the present study, we investigated evidence for cross-temporal changes in achievement-based g in a formal large-scale student assessment in Italy (i.e., the INVALSI assessment; N = 1,900,000+). Based on data of four school grades (i.e., grades 2, 5, 8, and 10) over 13 years (2010–2022), we observed little evidence for changes in achievement g in general. However, cross-temporal trajectories were differentiated according to school grade, indicating cross-temporal g decreases for lower grade students whilst changes for higher grade students were positive. These findings may be interpreted as tentative evidence for age-dependent achievement-g differentiation. The presently observed achievement g trajectory appears to be consistent with recently observed evidence for a potential stagnation or reversal of cognitive test score gains.