The over-arching aim of this multi-method study was to investigate the relations between children’s wellbeing and ‘school readiness’. There were four specific objectives: 1. To enrich understanding of the overlap between ‘school readiness’ and child wellbeing. 2. To examine characteristics that shape children’s wellbeing and ‘school readiness’. 3. To examine how family characteristics shape children’s wellbeing and ‘school readiness’. 4. To examine how children’s wellbeing and school readiness impact on caregiver wellbeing. Children and their caregivers in England were recruited to participate in a 12-month longitudinal study while the children were enrolled in Reception Year (i.e., the final year of the Early Years Foundation Stage in England) in Spring/Summer 2021. Children and their primary caregivers were seen on two occasions approximately 12 months apart (Mean Interval = 12.36 months, SD = 1.08 months) using a remote assessment protocol to mitigate the spread of Covid 19. Data collection was timed to take place when children had completed at least one term in Reception Year and then again after completing at least one term in Year 1. At both timepoints, following written consent, caregivers participated in a remote interview lasting approximately 20 minutes and then completed an online questionnaire pack. Children then participated in a remote testing session using videoconference software with a caregiver present. These sessions lasted approximately 45 – 60 minutes. Families received a voucher for participating in each wave of the study. Teachers were invited to complete a short questionnaire about each study child. Sample The initial plan for the current study was to track a pre-existing cohort of 200 children from the United Kingdom across the transition from Reception Year to Year 1 and to recruit an additional 250 children to enrich the sample. Restrictions due to the Covid-19 pandemic in 2020 and 2021 meant that the start date for the project was delayed and the opportunity to collect data from the pre-existing cohort was no longer possible as the cohort children had moved beyond Reception Year. We instead recruited a new sample of children for the current study. Monte Carlo simulations indicated that a sample size of 250 children would provide sufficient (.81 - .85) power to detect moderate-to-strong cross-lagged effects between two latent variables in a longitudinal model of two time points with three covariates. Children and their primary caregivers were recruited from across England in the Spring/Summer 2021 via mailings to primary schools and paid targeted social media advertising. To participate in the study, children were required to be enrolled in the first year of primary school in England (‘Reception’) and have no history of developmental delay. In England, children typically start the reception year of primary school in the September after their 4th birthday. The primary caregiver and participating child had to be able to communicate in English. We sought to recruit 250 children into the longitudinal study. Just under 500 caregivers expressed an interest in learning more about the study (N=494) and 260 of these families agreed to participate (52.6%). Of these 260 families, 5 families did not provide sufficient information to establish eligibility, 1 child was not attending Reception and 2 families planned to leave England before follow-up. At Time 1, 252 children (131 girls) aged 5.40 years (SD = 0.31) and their caregivers (92.7% mothers, M Age = 38.63 years, SD = 4.66) participated in the study. Children were predominantly from two-parent heterosexual households (92.1%). Caregivers were highly educated (83.7% had degree level education). On the subjective ladder of social status, 74.3% of caregivers rated themselves as 6/10 or above on a 10-point scale where 1 indicated the lowest levels of education, income, and status and 10 indicated the highest levels of education, income, and status. According to UK Census ethnic group categories, 80.5% of children were identified as ‘White’, 13.2% as ‘Mixed or multiple ethnicities’, 5.9% as ‘Asian’, 0.4% as ‘Black’. 223 out of 252 families participated at Time 1 and Time 2 (88.5%). Teacher questionnaires were available for 154 out of 223 children at Time 2 (69%) and Caregiver Questionnaires were available for 192 out of 223 children at Time 2 (86%).The over-arching aim of this multi-method study was to investigate the relations between children’s wellbeing and ‘school readiness’. There were four specific objectives: 1. To enrich understanding of the overlap between ‘school readiness’ and child wellbeing. 2. To examine characteristics that shape children’s wellbeing and ‘school readiness’. 3. To examine how family characteristics shape children’s wellbeing and ‘school readiness’. 4. To examine how children’s wellbeing and school readiness impact on caregiver wellbeing. Children and their caregivers in England were recruited to participate in a 12-month longitudinal study while the children were enrolled in Reception Year (i.e., the final year of the Early Years Foundation Stage in England) in Spring/Summer 2021. Children and their primary caregivers were seen on two occasions approximately 12 months apart (Mean Interval = 12.36 months, SD = 1.08 months) using a remote assessment protocol to mitigate the spread of Covid 19. Data collection was timed to take place when children had completed at least one term in Reception Year and then again after completing at least one term in Year 1. At both timepoints, following written consent, caregivers participated in a remote interview lasting approximately 20 minutes and then completed an online questionnaire pack. Children then participated in a remote testing session using videoconference software with a caregiver present. These sessions lasted approximately 45 – 60 minutes. Families received a voucher for participating in each wave of the study. Teachers were invited to complete a short questionnaire about each study child.

Data for this study were collected using multiple methods: structured caregiver interviews, standardized self-report questionnaires, structured observations, standardized assessments, structured child interviews. The protocols for the caregiver interviews, child testing sessions, caregiver questionnaires, and teacher questionnaire are included as separate documents.