This study investigated familial attachment-based processes in middle childhood, using 788 families (50.6% boys; 84.4% White), assessed six times from 4.5 years old to Grade 6. An adapted Random Intercept Cross-Lagged Panel Model revealed between-family associations among couple emotional intimacy, relationships with both parents, and child social skills ([beta] = 0.18-0.66). Within-family increases in child assertion and self-control prospectively predicted relationships with parents ([beta]s = 0.13), and parent-child relationships predicted various child social skills ([beta]s = 0.13-0.17). Couple emotional intimacy predicted child cooperation, assertion, and responsibility ([beta]s = 0.12-0.24) and father-child relationships in Grade 6 ([beta]s = 0.20-22) at the within-family level. Findings underscore a systemic consideration of attachment-based processes in the family.