This study investigated how well seventh-grade students (n = 1,434) evaluated the credibility of online information in science. The analysis examined the extent to which evaluation appeared to share aspects of other elements of online research and comprehension, including locating, synthesizing, and communicating. This study also investigated the extent to which prior knowledge, gender, socioeconomic status, and offline reading ability affected students' evaluation during online reading in science. Results suggest that evaluation is a unique and difficult dimension of online research and comprehension. Results also suggest that girls outperform boys and that students with greater prior knowledge and offline reading ability can better evaluate online information compared with those with less prior knowledge and offline reading ability.