Constructivist approaches to education embrace students' prior learning experiences and preference for learning in social environments. However, many postsecondary classes continue to embrace lecture-styles of teaching. This study sought to understand first-year students' perceptions of the mistakes instructors make in large lecture classes. Results indicated that the top 10 mistakes were as follows: (1) lack of engagement, (2) faulty assumptions related to students, (3) incomplete explanations, (4) flawed instructional delivery, (5) pedagogical errors, (6) inappropriate pace of instruction, (7) errors in the evaluation process, (8) confusing information, (9) ineffective use of teaching and learning technology, and (10) no mistakes (negative cases). Recommendations for correcting mistakes are noted, as are directions for future research.