The "cardinality principle" (CP) is a conceptual basis of counting collections meaningfully and provides a foundation for understanding other key aspects of numeracy, such as the successor principle or counting-on to determine sums. Unfortunately, little research has focused on how best to teach the CP. One suggestion is that modeling…

Although basing instruction on a learning trajectory (LT) is often recommended, there is little direct evidence to support the premise of a "LT approach"--that to be maximally meaningful, engaging, and effective, instruction is best presented one LT level beyond a child's present level of thinking. The present report serves to address…