This study modeled teacher–student relationship trajectories throughout elementary school to predict gains in achievement in an ethnic-diverse sample of 657 academically at-risk students (mean age = 6.57 years, SD = .39). Teacher reports of warmth and conflict were collected in Grades 1–5. Achievement was tested in Grades 1 and 6. For conflict, low-stable (normative), low-increasing, high-declining, and high-stable trajectories were found. For warmth, high-declining (normative) and low-increasing patterns were found. Children with early behavioral, academic, or social risks were underrepresented in the normative trajectory groups. Chronic conflict was most strongly associated with underachievement. Rising conflict but not declining Conflict coincided with underachievement. The probability of school failure increased as a function of the timing and length of time children were exposed to relational adversity.