Appropriate interpretation of assessment data requires an appreciation that tools are subject to measurement error. School psychologists recognize, at least on an intellectual level, that measures are imperfect--that test scores and other quantitative measures (e.g., rating scales, systematic behavioral observations) are best estimates of characteristic traits and behaviors, subject to a certain degree of uncertainty. Test publishers provide reliability data to establish the degree of measurement error associated with test scores so that practitioners can qualify findings accordingly. However, regard for measurement error can be compromised because (a) the reliability estimates used do not adequately reflect the extent of measurement error inherent "in the real world," and (b) school psychologists may lose sight of measurement error when interpreting and reporting assessment findings. The point of this article is not to imply that tests and measures have diminished value, but rather, that their results should be interpreted and reported with recognition of their actual level of reliability.