In this paper, we examine how prior knowledge impacts usability and efficacy reactions to object-oriented techniques. We develop research hypotheses based on the multiconstraint theory of analogical reasoning. We empirically test the hypotheses in an open learning setting. We observed a significant interaction effect: the subjects with prior knowledge on either data or process modeling technique perceived greater difficulty and less confidence in learning object-oriented techniques than novices as well as those who have prior knowledge on both structured techniques. Prior knowledge explained 19% of the variance in both usability and efficacy reactions and, as a common cause, partially explained their correlation.