ctivity and to enhance social skill development. When children play freely with materials that are intriguing and that also require physical exertion, we believe that they will spend more time engaging in the activity and thus also be more active for longer periods of time. When materials are large, a little unwieldy, or a bit heavy, it is possible that, in addition to expending more energy, and exerting greater effort, they will recruit help from other children, thus promoting social negotiation in the context of creative play (i.e., what can we do with these materials?). Play also offers opportunities for children to take manageable risks and to experience the benefits of a variety of challenges (e.g., motor, social, emotional and cognitive). The playground based intervention presented here is aimed at appealing to children's inherent will to play, rather than imposing a structured program or regimen.
Prevention strategies that target the population as a whole, rather than focussing only on children at risk are preferable. It is difficult to identify who is at risk and all children benefit from increased activity independent of body composition and interest . Thus programs conducted at schools can be highly beneficial.
Previous studies have supported play and changes to the playground as a way of increasing activity. In the UK, painting lines on the playground to promote active games resulted in small but significant and lasting increases in children's physical activity [49–51]. Placing play equipment and activity cards on school playgrounds in Belgium significantly increased the children's moderate to vigorous physical activity (MVPA) . Similar results were found in North Carolina where portable play equipment, including skipping ropes and hula hoops, at day care facilities increased physical activity . Turning a Canadian school playground into a natural play space also increased physical activity significantly . The same group of researchers also found that a higher percentage of children were engaged in MVPA 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