Student-teacher relationships (STRs) and socioeconomic status (SES) are two widely studied variables that have been found to predict reading achievement in the early grades. The current study extends the literature by investigating the interaction between STRs, measured using the STR Scale completed by teachers, and SES on reading achievement using a nationally representative data set. The study included approximately 8,380 first-grade students and 2,930 teachers, from 860 schools, representing a weighted sample of 3.15 million students. Results from multilevel modeling that controlled for student-, teacher-, and school-level factors found that both STRs and SES were strongly associated with student reading achievement. There was also a statistically significant interaction between close STRs and SES on reading achievement, suggesting that less conflictual STRs were associated with increased reading achievement scores for all students, but were particularly beneficial for students from low SES backgrounds. Educational implications are provided.