Classification skills, so foundational to science, must be taught. While children have a passion and drive to organize and categorize their experiences, sometimes the way they organize them doesn’t lead to a worthwhile or accurate scientific understanding. Just as putting a pencil in the hands of a child doesn’t automatically teach them to write, having a child sort rocks won’t lead to an understanding of classification. The articles in this issue aim to help you teach students how to classify successfully and with purpose.