Abstract
The purpose of this research was to estimate the difficulty levels of tasks in arithmetic calculations in order to investigate the optimum arrangement of the tasks for teaching. The six forms of tests were constructed so that each form should include items of the calculation tasks for each grade at the elementary school level, and they were administered to 2822 pupils. By means of the two-parameter logistic model, the item parameters were estimated for the 221 items contained in the six forms of tests. The rusults showed that the model was satisfactorily fitted to the data. Furthermore, inappropriateness of conventional order of calculation tasks in teaching was also discussed.
