Researchers have studied academic self-concept and its relationship to academic achievement extensively, but not in the Spanish heritage language context. Using measures of reading, writing, and spelling performance, I investigate the relation between self-concept and performance and whether self-concept can predict performance scores. I obtained measures of self-perceptions of abilities and attitudes from 281 students in 4 Spanish heritage language course levels. The results indicated that self-concept increased as course level increased. Self-perceptions related significantly to students' performance in all subcompetencies except reading and were predictors of performance scores. Cluster analysis showed that students with the highest level of self-concept also had the highest reading, writing, and spelling scores and the most positive attitudes. This study demonstrates that self-concept plays a significant role in student literacy performance. Thus, practitioners should focus on helping students improve self-perceptions for their impact on literacy development and their role in overcoming learning difficulties.