Performance on five logical, spatial and formal tasks was used to make inferences about the reasoning structures of the subjects. The tasks used were: seriation matrix, tilt of a cone, location of a point in two and three dimensions, flexible rods and projection of shadows. Three research questions were asked: first, what is the general level of performance; second, are there grade level differences; and third, are there gender differences in task performance. The subjects were 101 middle and high school students chosen at random from the school population. Each task was given in an individual interview. Findings include grade level differences in performance and gender differences in performance on one of the tasks. Implications for classroom teachers were proposed.