Reading for understanding is a challenging task for many upper elementary struggling readers, and their attitudes toward such challenges can make a difference in their subsequent engagement and reading achievement. Mindset and achievement goals provide a useful explanatory framework for understanding struggling readers' engagement and reading comprehension. This study examined the extent to which mindset and achievement goals are associated with reading comprehension; as well as the mechanism through which engagement mediates this relation, controlling for the effects of vocabulary, word recognition, and limited English proficiency status. Structural equation modeling of four and fifth grade struggling readers (N = 107) demonstrated the importance of achievement goals in predicting reading comprehension. Effects of mindset on engagement and reading comprehension were completely mediated by mastery and performance-avoidance goals; further, these goals had indirect relations to reading comprehension through emotional engagement. Performance-approach goals had a direct, negative relation to reading comprehension. Findings highlight the importance of including motivational variables in understanding sources of individual differences in reading comprehension for struggling readers.