Missing data are a common problem in a variety of measurement settings, including responses to items on both cognitive and affective assessments. Researchers have shown that such missing data may create problems in the estimation of item difficulty parameters in the Item Response Theory (IRT) context, particularly if they are ignored. At the same…

Proposes a theory of cognitive processes in doing and learning place value arithmetic. Discusses a computer model that simulates the learning of multicolumn subtraction under one-on-one tutoring to measure the relative difficulty of two methods of subtraction. The model predicts that regrouping is more difficult to learn than an alternative…