Source-based writing, including summary writing, is a key skill for academic literacy and required at many universities. For undergraduate English as a Second Language (ESL) students, learning to write from sources can be a challenging process. Source-based texts were analyzed from two groups of undergraduate ESL students at different stages of their university education, one group in a lower 100-level composition course and the other group in a higher 300-level composition course. The summaries were analyzed quantitatively and qualitatively for length, textual similarity to the source text, inclusion of key source text propositions, references to the source text, types of agents used from source text propositions, and reporting phrases used for source text propositions. While the 300-level summaries were more concise than the 100-level summaries, the 300-level summaries exhibited a greater degree of textual similarity to the source text. The 100-level summaries are more successful in reporting smaller source text propositions, but the 300-level summaries are more successful in attributing propositions to the source text. In terms of reporting propositions from the source text, the 100-level and 300-level summaries are similar in amounts and types of reporting in the texts, but differ more in which reporting phrases are used frequently. Overall, the differences between the 100-level and 300-level summaries are complex and nuanced.