Extensive literature highlights positive outcomes experienced by students whose parents and teachers have strong relationships, but less is known about the factors that influence parent-teacher relationship strength. Using data from "The Impact of Grade Retention: A Developmental Approach," we identify parent-level predictors of the developmental trajectories of seven dimensions of parent and teacher ratings of relationship strength and evaluate the association between relationship strength and students' academic performance in grades 1-8. Results show that parent acculturation, parent-teacher ethnic concordance, and beliefs about children's educational attainment predict trajectories of parent and teacher ratings of relationship strength. Relationship strength is both positively and negatively related to student reading and math performance. Results identify unique patterns of predictors for parent and teacher ratings of relationship strength and suggest that strong relationships can be related to student academic success or underperformance. Implications of these findings for researchers and practitioners are discussed.