We developed an experiment that was a little simpler for monkeys to perform than the typical sorting task used in a dimensional category card sort to test category switching. In this case, in each trial, a child or monkey is shown two cards, like those above (red truck, blue boat). They are encouraged to pick one, and if it represents the correct category, they get rewarded, either with a sticker in the case of a toddler, or with a cheerio treat in the case of a monkey. We first train one dimension, like color, and one type, like red, as the correct one to choose. Then, when subjects show 80% correct performance, we suddenly switch criterion without any information shared to a different type in the same dimension (intradimensional switch, or “blue” in this case) or to a different type in a different dimension (an interdimensional switch, in this case, to shape, or “truck”). Three-year-olds struggle to make an interdimensional switch, but 5-year olds can switch intradimensionally or interdimensionally with ease. So can adult cotton top tamarins.