The authors investigated the performance on simple multiplication and division problems of 8-year-old children longitudinally to determine the developmental trajectories of both operations. Twice a year, during 2 consecutive school years, children performed a multiplication and division verification task and a number-matching task. All effects that were observed in multiplication performance (problem size, 5, and tie effect and Tie x Size interaction) were also observed in division performance. The developmental trajectories of these effects are described. The authors observed strong developmental parallels between both operations. These results are in line with strongly interconnected memory networks for multiplication and division facts, at least in young children. The results of the number-matching task showed that the interference effect developed differently for multiplication and division, indicating that automatic activation spreading from division operands to division answers is not at work in children of that age. (Contains 3 figures, 7 tables, and 3 footnotes.)