The authors examined how motivational and cognitive variables predict reading comprehension, and whether each predictor variable adds unique explanatory power when statistically controlling for the others. Fourth-grade students (N = 205) completed measures of reading comprehension in September and December of the same year, and measures of background knowledge and cognitive strategy use in December. Teachers rated internal reading motivation of each student. Results from multiple regression analyses showed that motivation, background knowledge, and cognitive strategy-use made significant, independent contributions to children's reading comprehension when the other predictor variables were controlled. Further analyses showed the same cognitive and motivational variables predicted growth over a 3-month period in reading comprehension. Possible explanations of the observed relations between motivation, cognitive variables, and reading comprehension are presented.