I am an assistant professor at an undergraduate college in India. I teach a rigorous compulsory course in microeconomics, requiring some intermediate-advanced math knowledge. There is no add/drop option at my University/college, nor is there an option to take a course in a later semester. I don't decide the syllabus or the final exam--it is set centrally. We are a publicly funded University and have a diverse set of students.
General math preparation in my country is low, due to poor schooling standards and sometimes, students are not clear about basic concepts: for example, in a third semester intermediate microeconomics course, some of them don't know how to write the (linear) equation of a budget frontier (something taught to them in the first semester). Unless they understand such things, it is impossible for them to grasp the rest of the material, since all topics are related. Is it my responsibility to explain concepts taught in introductory-level courses? I welcome all questions and have a generally amicable attitude, so students don't feel intimidated in getting a clarification.
However, I do get frustrated sometimes when having to answer something very basic, that too repeatedly. I get glowing feedback for most of my courses, but despite being appreciated for my effort and the clarity of explanation, a group of students (around 20% of the class) repeatedly under-performs, which upsets me a lot. How much should I hold students responsible for their learning?