Background: Valid motor development sequences show the various behaviors that children display as they progress toward competence in specific motor skills. Teachers can use these sequences to observe informally or formally assess their students. While longitudinal study is ultimately required to validate developmental sequences, there are earlier, pre-longitudinal steps that can be used to screen hypothesized sequences to see if they are worthy of the time and expense of longitudinal study. These same steps can also provide teachers with preliminary tools for observation/assessment. Purpose: At the request of physical educators in a midwestern suburb in the United States, the investigators screened developmental sequences for the action of arms and legs in self-turned rope jumping. The goal was to create a preliminary assessment tool that could be used in physical education classes. Participants: The physical educators took videos of 216 children attempting to jump rope. The children were 5-10 years of age. Data analysis: The investigators categorized the videos using the hypothesized developmental sequences as a checklist. The incidence of each level in the sequences was then graphed to see if the percentages of occurrence rose and fell across age as would be expected if the levels were developmentally valid. The investigators also looked at whether children who varied their behavior across trials varied only to adjacent levels in the sequences. Results: Results indicated that one hypothesized arm category was not developmental, and two leg categories needed further study in younger children. Based on these results, the investigators modified the proposed sequences and provided decision rules so teachers could use them as preliminary observation/assessment tools.