Differences in cognitive ability determine developmental trajectories across the lifespan, affecting socioeconomic, psychological, and health outcomes. Children from disadvantaged socioeconomic status (SES) families show lower cognitive ability and reduced cognitive growth (i.e. ability gains over time) compared to their high SES peers. However, the mechanisms that underlie the SES-growth association are not fully understood. The proposed research investigates how and to what extent 3 aspects of children's lives - (1) dietary patterns, (2) preschool experiences, and (3) activity engagements - account for SES-related growth differences.

(1) Dietary Patterns. Diets directly impact cognitive function because they are the main source for micronutrients (e.g. vitamins and antioxidants) that enable enzymatic reactions and neurotransmitter synthesis in the brain. However, several diet characteristics have rarely been addressed in research, for example meal types (e.g. snack), times (e.g. breakfast), and preparation method (e.g. prefabricated). Likewise, no previous research has looked at the influence that children's drinking habits (e.g. milk, sugary drinks) may have for cognitive development.

(2) School Experiences. SES-related differences in primary school performance tend to increase or at least persist over time, with disadvantaged children continuing at lower quality secondary schools and obtaining fewer educational qualifications. Preschool attendance may reduce this achievement gap because it provides disadvantaged children with better learning environments than they receive otherwise. The benefits of preschool have not been studied in Britain, where several preschool types exist (e.g. nursery or childcare centre).

(3) Activity Engagement: The availability of activity engagement opportunities, for example music lessons or sport clubs, leads to better primary school achievement16 and is thought to benefit children's cognitive growth. High SES families encourage more frequent and diverse activity participation than do low SES families in the United States16 but these findings have yet to be replicated in Britain. Also, it is unclear if it is the quantity, quality or type of activity engagement that make the difference for children's cognitive development.

Methods: Data will be synchronized across 4 longitudinal, British cohort studies, including the British Cohort Study 1970 (BCS), the Growing Up in Scotland study (GUS), the Millennium Cohort Study (MCS), and the Avon Longitudinal Study of Parents and Children (ALSPAC). The cohorts comprise of large samples, representative of the British population, and span generations from 1970 to 2005 (Table 1). Thus, they allow for (1) exploring and (2) replicating effects of dietary patterns, preschool experiences and activity engagements (herein variable complexes) on cognitive growth, as well as for (3) analyzing possible generation-specific effects. In each cohort study, participants were assessed at least 3 times on cognitive ability, enabling (4) latent growth curve modelling of ability trajectories. They also completed several, mostly repeated measures for all variable complexes, permitting (5) in-depth investigations of their characteristics and continuity over time.