This study examined relationships between reading comprehension, known predictors of reading comprehension (i.e., cognitive flexibility, fluency, reading motivation and attitude, vocabulary), and graphical device comprehension. One-hundred fifty-six third graders completed assessments of known predictor variables and an assessment tapping comprehension of graphical devices commonly found in age-appropriate informational texts: captioned pictures, insets, surface diagrams, cross-sectional diagrams, flow charts, timelines, and tables. Graphical device comprehension was strongly correlated with reading comprehension, rs = 0.49, p (one-tailed) < 0.01. Regression analyses, including known and new variables, revealed that graphical device comprehension accounted for 12.81% of the resulting standardized model predicting general reading comprehension.