A longitudinal approach was used to examine the effects of parental task-intrinsic and task-extrinsic motivational practices on academic intrinsic motivation in the subject areas of math and science. Parental task-intrinsic practices comprise encouragement of children's pleasure and engagement in the learning process, whereas task-extrinsic practices comprise parents' provision of external rewards and consequences contingent on children's task performance. A conditional latent curve model was fit to data from the Fullerton Longitudinal Study (A. W. Gottfried, A. E. Gottfried, & D. W. Guerin, 2006), with academic intrinsic motivation in math and science assessed from ages 9 to 17 and parental motivational practices measured when children were age 9. The results indicated that task-intrinsic practices were beneficial with regard to children's initial levels of motivation at age 9 as well as with regard to motivational decline through age 17. Conversely, parents' use of task-extrinsic practices was adverse with regard to children's motivation both at age 9 and across the 8-year interval. Theoretical implications of the findings with regard to academic intrinsic motivation are discussed. (Contains 2 figures, 3 tables, and 2 footnotes.)