British Educational Research Journal

The objective of this study was to examine how individual interest and knowledge acquisition are causally related. Three hypotheses were tested using a cross‐lagged panel analysis (N = 186) and two quasi‐experimental studies (N = 68 and N = 108) involving students from schools in Singapore. The first hypothesis is the broadly shared standard assumption on the relation between individual interest and knowledge: the more an individual is interested in a topic, the more (s)he is willing to engage in learning. An alternative hypothesis assumes that individual interest is not the cause but the consequence of the process of learning: individual interest as an affective by‐product of learning. Finally, a third possibility is that interest and knowledge influence each other reciprocally. The results supported the affective‐by‐product hypothesis. Our findings seem at variance with commonly held conceptions that being interested guides knowledge attainment. The implications of these findings for interest research are discussed.