A few students always exceed our expectations, a few dramatically fail to meet them, and most pretty much achieve what we ask of them. Within limits, then, raising our expectations and communicating them effectively raises our students' achievement. Knowing just how high we can realistically set our expectations requires knowing our students. Experience helps here, and so does data gathering. Good practice respects diverse talents and ways of learning.
Students differ along many important dimensions.
Each brings a distinct set of strengths and challenges to the role of students. The simplistic, and pragmatically unrealistic, response to this observation is to try to match teaching styles with learning styles. What we can do is try to make our teaching as complex as our students are. Metaphorically, I think this principle calls for buffet teaching instead of fixed menus. To the extent that there exists multiple ways of learning within our discipline, and multiple ways of demonstrating that learning, we should represent that variety within our classes.