 on green areas and on fixed playground equipment than on sporting courts and other courtyards .
A few previous researchers have introduced unstructured materials to school playgrounds and studied the effect on social interaction and play. One of them is a Play Pods study, carried out in Bristol from 2006 to 2009 . The overall impression of the outcomes, determined by observations and interviews with children and school staff, was very positive. The researchers observed that the loose items improved children's participation, decision making skills and their control of play within school setting, as well as improved access for all children to inclusive play opportunities. We build on studies such as this with quantitative data.
Aims and hypotheses
Child-based intervention: Recycled unstructured materials are placed on the school playground with the aim of increasing physical activity and social skills through unstructured free play.
Adult-based intervention: Risk reframing sessions held with parents and teachers with the aim of exploring the benefits of allowing children to engage in activities with uncertain outcomes.
Overall study design
Participants and recruitment
Catholic co-educational primary schools are approached to participate in the study, through emails, phone calls and on-site visits to the principal and/or assistant principal. The schools are located within a 30 km radius of the University of Sydney's Health Sciences campus at Lidcombe, near Sydney. Recruitment continues until 12 schools agree to participate.
All participating schools must agree to be randomised into the control or intervention group and refrain from engaging in other new interventions designed to increase activity levels. They continue with normal recess and physical education. There are no exclusion criteria.
Within each school, a random sample of children is invited to participate. Children are selected using the following procedure: To maintain confidentiality, schools assign each of their Kindergarten and Year 1 students (aged 5 to 7 years) a number. Schools are then presented with a set of randomly generated numbers. School staff approach children assigned to the random numbers until 20 students and their parents consent to participate. Data are gathered on country of birth of children and parents as well as languages spoken. Families are approached only if the parents can speak and understand spoken and written English to a degree sufficient to allow them to complete the questionnaires and participate in the risk reframing intervention. Children are included regardless of known disability.
Sample size calculation involves deciding on both the number of schools (clusters) and number of children per school. The desired number of schools provides sufficient cluster-level data for subsequent analyses but, at the same time, is manageable in terms of implementation and data collection. We have selected 12 schools (6 control, 6 intervention) to meet these criteria.
The number of children needed per school is estimated by considering the amount of change from the intervention and correcting for the possibility that children at the same school affect one another's activity levels (determined by intra-cluster correlation [ICC]) We estimated the effect size from the intervention conservatively at 0.5 standard deviations (SD) based on a report that young children engage in moderate to vigorous playground activity 26% of the time and that 40% would be a realistic health-promoting target .
With p = 0.05, power = 80% and an ICC of .04, we require 18 children per school to show that an effect size of 0.5 SD is significant between groups. This reflects a 68% inflation in sample size over the number that would be required if no adjustment were made for cluster effect (64 vs. 108 participants/group).
The 12 participating schools are randomly assigned to either the control or intervention cluster. Randomisation is performed prior to the commencement of the study by a researcher unrelated to the study; researchers are blinded to school allocation until af