Students in grades 5, 8, 11, and college were administered Piagetian tasks dealing with horizontals and verticals. The tasks were the bottle task, the pendulum task, and the faucet task. The results disagreed with Piaget's suggested timetable. Since the horizontal task results did not yield a majority of correct predictions for any of the groups, this research does not conclusively establish that a majority of individuals ever attain this ability. A follow-up interview validated the data and also provided evidence that the use of coordinate systems of reference in the plane develops prior to the ability to use spatial reference systems. (Author/MP)