This study evaluated a new measure for analyzing the process of children's problem solving in a series completion task. This measure focused on a process that we entitled the "Grouping of Answer Pieces" (GAP) that was employed to provide information on problem representation and restructuring. The task was conducted using an electronic tangible interface, to allow for both natural manipulation of physical materials by the children, and computer monitoring of the process. The task was administered to 88 primary school children from grade 2 (M = 8.2 years, SD = 0.50). GAP was a moderate predictor of accuracy on the series completion task. Averaged over multiple items, GAP, verbalizations and time measures were related to accuracy. On an item level, however, GAP was the only process measure related to item solving success, and this relationship was mediated by item difficulty. Further research is needed to investigate the precise relationship between problem solving and GAP