Older but not younger preschoolers use efficiency to evaluate how well goals are completed.

Instrumental rationality dictates that goals should be completed efficiently rather than inefficiently. Here, we examined how young children come to use efficiency to evaluate how well goals are completed. Across a series of experiments, we showed children aged 3-7 (total N = 618; 48% female and 52% male; tested in a predominantly White region) scenarios where pairs of agents approached objects using paths that varied in length and efficiency, and then asked children which agent did a better job. In Experiments 1A and 1B, children aged 3 and 4 evaluated the agents using path length, but not efficiency. In Experiments 2A, 2B, and 3, children used path length to assess which agent did a better job from around age 4. But children only used efficiency from age 5 or later. These findings suggest that children's explicit judgments are not guided by the norm for efficiency, and Experiment 4 provides evidence that this late development is not an artifact of methodological problems. This developmental pattern might arise from limits in children's ability to make counterfactual judgments about what agents could have done. (PsycInfo Database Record (c) 2026 APA, all rights reserved).