Background The mainstream randomized clinical trial is not always feasible in a school setting. There might be practical and ethical issues that make dividing school classes into an intervention and a control group impossible or undesirable, and there is a need to explore the validity of alternative designs and analyses.
Methods An alternative to a randomized clinical trial in a physical performance experiment at a school is introduced and evaluated. The before-intervention data are utilized as control data for the intervention data in addition to adjust for pre-intervention differences. The strict class year structure of school data makes this possible. In a rural school in inland Norway, all school children joined the project of walking in a rugged terrain outside school for 20 min every school day during one school year. Measurements of low back static endurance, hamstrings flexibility, standing balance and cardiovascular fitness were made before and after the intervention. As intervention and ‘aging’ were confounded, the special use of the pre-intervention data, ‘age-adjusted’, is proposed to solve this issue. A comparison with having an independent control group is performed.
Results The alternative analysing method is judged to yield valid results without having an independent control group. The age-adjusted analyses showed 11% increase in low back static endurance, 8% increase in hamstrings flexibility, 69% increase in balance and 6–13% increase in cardiovascular fitness. The effects were largest among those children who had the lowest performances before the intervention.
Conclusion The introduced statistical methods display that, in a school population, evaluations from an experiment can be made without an independent control group. A 20-min walk during school time for 1 year seemed to improve physical performance.