Learners of English as a Second Language (L2) need to develop their ability to incorporate ideas from different sources to support their arguments to be successful in higher education. Recently, there has been a growing trend towards assessing test-takers’ ability to summarize different sources (e.g., audio lectures, texts, and charts). While integrated tasks are often centered around read-to-write tasks, there is increasing interest in listen-to-write tasks to test summarization skills. This study aimed to deepen our understanding of how listening proficiency affects listen-to-write summarization tasks. In this mixed-methods study, we used an eye-tracking device to monitor test-takers’ eye movements during listen-to-summarize tasks across different areas (n = 20) and tested them twice for different levels of difficulty. This was followed by the collection and analysis of qualitative data from the survey, stimulated recall interviews, and essays produced by test takers to compare the different strategies they applied to the two listening tests. The findings revealed that a more challenging listening task required significant cognitive effort to recall words from memory for summary production, causing the participant to pause longer on the screen. The Chi-square test showed that only the summarization task with the more challenging listening material predicted the result of the listening quiz that they took. Eye-tracking results suggest that listeners used different strategies depending on the task difficulty. Such empirical findings offer important implications for understanding the strategies that listeners use for listen-to-summarize tasks that involve note-taking to process information and help improve teaching methods in EFL classrooms.