Because literacy skills are critical for most academic subject matters, researchers have become increasingly interested in understanding children's motivation in this domain as a way to increase academic success. In this study, we extend previous work by looking at the heterogeneity of children's motivational changes in literacy across Grades 1-12. We used a cross-sequential design based on 3 different cohorts of children (N = 655) coming from 10 public elementary schools. Data were collected over an 8-year period (1988-1996) starting when children were in 1st, 2nd, and 4th grades. Using multiple-process growth mixture modeling, we identified 7 groups of children showing distinct trajectories of change in literacy subjective task value and ability self-concept across school years. For all children, ability self-concept and subjective task value decreased between Grade 1 and Grade 12; however, this decline was more apparent for some youths than for others. Our findings suggest the importance of school-based interventions that aim to prevent decreases in student motivation for literacy over time and that focus on the early detection of children at risk for dramatic declines. (Contains 4 tables, 1 footnote and 1 figure.)