Attentional inhibition is the ability to suppress task-irrelevant cognitive processing and ignore salient yet irrelevant features of the situation. However, it remains unclear whether inhibition is a singular function. Prominent are four proposals: a one-factor model of inhibition, an attentional model of inhibition, a response- versus cognitive-inhibition taxonomy, and an effortful- versus automatic-inhibition taxonomy. To evaluate these models, we administered nine inhibition and three attention tasks to 113 adults (Study 1) and 109 children (Study 2). Inhibition models were evaluated using confirmatory factor analysis after statistically controlling for attentional activation. Subsequent age analyses investigated whether inhibition tasks and factors related differentially to age, yielding distinct developmental trajectories. Results provide converging evidence for the automatic-effortful taxonomy - a distinction masked when the contribution of attention is ignored. These results highlight problems of isolated task-based characterizations of inhibition without a theoretical foundation based on evidence from multiple methodologies and populations.