The knowledge-gap hypothesis of Tichenor, Donohue, and Olien (1970) states that people from the higher socioeconomic segments of society acquire information at a faster rate than people from the lower socioeconomic segments. The consequence is a growing knowledge gap between the high and low segments. The present study investigates some potential causes for this knowledge-gap phenomenon by means of data sets from evaluation studies of 3 mass-media information campaigns. The observed differences in knowledge between low and highly educated respondents could partly be explained by differences in the attention paid to the campaigns but not by differences in information processing.