A section of the secondary chemistry curriculum was analyzed to determine the level of cognitive demand of the various aspects of the selected topic. Piagetian levels of thinking of 71 pupils were initially assessed by two group tests, a unit on the mole was taught, and guidelines were used to estimate the level of cognitive operations required by each concept and problem type in the unit. Results of a 23-item test were used to compare the estimated level of cognitive demand of each test item with the Piagetian cognitive level of pupils who were able to answer the item correctly. It was found that pupil cognitive level was positively associated with overall unit test score and with percent success on all test items. Predicted levels of cognitive demand were confirmed for eight items and were within one level for nine additional items.