This study examined the accuracy with which preschool teachers judge their students\u27 alphabetic knowledge. It also explored the types of information teachers used to inform their judgments. Thirteen teachers participating in an Early Reading First project judged whether preschool students in their classrooms would respond correctly or incorrectly to items on a norm-referenced test of alphabetic knowledge. These judgments were then compared to students\u27 actual performance on the same items and the percent agreement was calculated. Teachers correctly judged their students\u27 item-by-item achievement with 70.1% accuracy, a level that is comparable to that of K-12 teachers in previous research. Their judgment accuracy was greater for higher and lower performing students than for average students, and for easier than more difficult items. Teachers were also interviewed about the sources of information they used to formulate their judgments. Results indicated that teachers tended to rely on knowledge of the taught curriculum and on task analysis most frequently, less often on direct observation or assessment of students, and rarely on the non-literacy characteristics of students (e.g., general ability, behavior); however, teachers\u27 use of specific sources of data was not related to their overall judgment accuracy. The present study represents the first examination of preschool teachers\u27 item-by-item judgments, and is the first attempt to account for the types of data that inform those judgments. Future research should extend these findings to teacher judgments of other indicators of early reading and mathematics