Early efforts to apply knowledge of dialect differences to reading stressed the importance of the distinction between differences in pronunciation and mistakes in reading. This study develops a method of estimating the probability that a given oral reading that deviates from the text is a true reading error by observing the semantic impact of the given pronunciation on the child's reading of the text that immediately follows. A diagnostic oral reading test was administered to 627 children who scored in the 33rd percentile range and below on state-mandated assessments in reading in Philadelphia, Pennsylvania, Atlanta, Georgia, and California elementary schools. Subjects were African American, European American, and Latino, including Latinos who learned to read in Spanish and in English first. For 12 types of dialect-related deviations from the text that were studied, the error rates in reading the following text were calculated for correct readings, incorrect readings, and potential errors. For African Americans, many of these potential errors behaved like correct readings. The opposite pattern was found for Latinos who learned to read in Spanish first: most types of potential errors showed the high percentage of following errors that is characteristic of true errors. This article considers the question "What is a reading error?" based on a study of 627 struggling readers in inner city elementary schools in Philadelphia, Pennsylvania, Atlanta, Georgia, and California. 1 The work reported here is drawn from an initial assessment of reading skills in research on the effectiveness of an individualized reading program for raising reading levels. It provides a general answer to the question of how to define a reading error, and a method for determining the answer for any specific type. It also demonstrates differences in the profiles of reading errors of different groups who come to the task of reading English with different dialects and language backgrounds, and the probability that a given deviation from the standard reading of a text represents a failure to properly decode and comprehend that text.Early research on dialect differences in the pronunciation of English pointed to the consequence of these differences for reading research. Initial studies of The research problems addressed here spring from the observed difficulty in distinguishing differences in pronunciation from the wrong selections of the word intended in the text. To this end, we initially distinguish "clear errors," where the wrong word has clearly been identified, from "potential errors," which may only represent differences in pronunciation of the target word. We are particularly interested in potential errors that are related to dialect differences and classify them by the type of phonological or grammatical elements involved.Three research questions are addressed in the work described here. First, can reading errors be distinguished from differences in pronunciation in the oral productions of struggling readers? To answer this question, we argue...