How does conceptual structure of external representations contribute to learning? This investigation considered the influence of generative concept sorting and of external structure information moderated by perceived difficulty. In Study 1, undergraduate students completed a perceived difficulty survey and comprehension pretest, then a sorting task, and finally a comprehension posttest. Results showed that both perceived difficulty and comprehension pretest significantly predicted comprehension posttest performance. Learners who perceived that history is difficult attained significantly greater posttest scores and had more expert-like networks. In Study 2, participants completed the same perceived difficulty survey and comprehension pretest, then were randomly assigned to read a text with different external structure support, either an expert network or an equivalent outline of the text, and finally all completed the same sorting task posttest and a comprehension posttest. In Study 2, there was no significant difference for external structure support on posttest comprehension (outline = network), but reading with an outline led to a linear conceptual structure that matched the topic order of the text while reading with a network led to a more expert-like relational structure. As in Study 1, comprehension pretest and perceived difficulty significantly predicted posttest performance, but in contrast to Study 1, learners who perceived that history is easy attained significantly greater posttest scores. Practitioners should consider using generative sorting tasks when relearning history content. For theory building purposes, post-reading mental representations matched the form of the external representation used when reading, thus the conceptual structure of the external representation should be considered in future research.