Exposure or age? The effect of additional CLIL instruction on young learners’ grammatical complexity while performing an oral task

The purported foreign language gains of content and language integrated learning (CLIL) over traditional EFL (English as a foreign language) programs with young learners are still unclear. Specifically, little is known about how CLIL time and timing impact grammatical complexity. Additionally, mediating factors such as socioeconomic status (SES) and extramural exposure have been rarely controlled in the existing literature. This study analysed grammatical complexity in four groups of young learners in Spain ( n = 108) during an oral task. The sample comprised: (1) an EFL-only group (1,766 EFL hours), (2) a low-exposure CLIL group (1,766 EFL hours + 707 CLIL hours), (3) a high-exposure CLIL group (1,766 EFL hours + 2,473 CLIL hours), and (4) a younger high-exposure CLIL group (1,545 EFL hours + 2,164 CLIL hours). All groups were matched for SES and extramural exposure. The analysis included independent ratings and computational measures of overall sentence complexity, subordination, and coordination. Distribution, Kruskal–Wallis and post-hoc tests were conducted. Results showed significant differences in favour of the high-exposure groups over the EFL-only group in the ratings and in two of the computational measures: overall sentence complexity and subordination. This evidence highlights the potential of high-exposure CLIL to supplement grammatical instruction in EFL programs. Our results also suggest that the comparatively higher exposure of the younger high-exposure CLIL group has the potential to override the one-year cognitive advantage of the older, EFL-only learners.