The test‐taking behaviour of some examinees may be so unusual that their test scores cannot be regarded as appropriate measures of their ability. Appropriateness measurement is a model‐based approach to the problem of identifying these test scores. The intuitions and basic theory supporting appropriateness measurement are presented together with a critical review of earlier work and a series of interrelated experiments. We conclude that appropriateness measurement techniques are robust to errors in parameter estimation and robust to the presence of unidentified aberrant examinees in the test norming sample. In addition, the frequently criticized ‘three‐parameter logistic’ latent trait model was found to be adequate for the detection of spuriously low scores in actual