Previous research has identified various factors that contribute to readers' comprehension of expository texts, including strategy expertise, language proficiency, prior knowledge, and more recently, readers' beliefs about knowledge. This study addresses the need to understand the relative contributions of these predictors to readers' comprehension of multiple texts and the processes used by readers to make sense of texts. Eighty-three students (grades 5-7) participated in this mixed-methods study. The sample consisted of monolingual students and emergent and proficient bilingual students who completed measures of expository comprehension, strategic knowledge and awareness, English-language proficiency, prior content knowledge, and epistemic beliefs. Ten bilingual students from this sample also completed a think-aloud protocol to allow for close examination of their meaning-making processes. In a multiple regression analysis, English-language proficiency was the strongest predictor of comprehension, followed by content knowledge. Strategy knowledge and awareness and epistemic beliefs were not related to multiple-text comprehension in the model. The relationship between English-language proficiency and comprehension was stronger for bilingual students than for monolingual students. Students in the think-aloud sample demonstrated emergent knowledge of processes of disciplinary reading of multiple texts, including metacognitive monitoring, theorizing authorial identity, and intertextual integration, while also displaying a tendency to defer to institutionalized authority when evaluating credibility of the texts. The findings provide directions for future research on the way young adolescents comprehend and learn from expository texts in the discipline of science.