 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 after baseline data collection at the relevant school. The schools are informed of their allocated treatment after baseline data collection.
Unstructured materials are introduced on the school playgrounds to be used during recess. The materials are selected to conform to seven principles: 1. no obvious play value; 2. encourage cooperative, gross motor play; 3. have multiple uses; 4. can be used in challenging, creative and uncertain ways; 5. provide interesting sensory experiences (e.g., from touch or movement); 6. inherent hazards can easily be seen/managed by a child; 7. are, or are made from, re-cycled materials. Examples of items include car tyres, milk crates, and cardboard boxes; in some cases these are reinforced or made more water resistant (e.g., by drilling tyres or covering cardboard with plastic tape). Some items, such as crash mats, are fabricated from recycled objects. All materials are checked for safety characteristics and child-proofed; all meet Australian standards for playground materials. New materials are introduced periodically to replace broken objects or to complement existing objects. Maintenance of the materials is the responsibility of researchers in collaboration with each school community but school staff must agree to remove materials that are broken or being used in unsafe ways.
This intervention runs in each intervention school over 2 terms (13 weeks total), during which time children are able to use and play freely with the items. The materials are for the use of all children at the school, independent of project consent.
Adult intervention: Risk Reframing
Teachers and parents of participating children from the intervention schools are asked to participate in a 2-hour group intervention. The adults participate in small "task groups" (n = 6-8) as well as large whole-group discussions (N = 18-24) to examine their own experiences of free play and their beliefs regarding the benefits and risks associated with active play. Discussions focus on similarities and differences of parents' and