We collected data at a large, very selective public university on what math and science instructors felt was the biggest barrier to their students' learning. We also determined the extent of each instructor's use of research-based effective teaching methods. Instructors using fewer effective methods were more likely to say the greatest barrier to student learning was the internal deficiencies of the students (the "fundamental attribution error"). They listed deficiencies such as poor preparation and work ethic. In total, 37% of the instructor attributions were to student deficiencies, but this fraction varied dramatically between departments.