What does it mean to be a 'good' student according to the commonsense?
It is suggested by Kumashiro that a good student follows the ideal 'good', listening, playing, creating as the teacher outlines is acceptable. This can change from each teachers expectation but he gives examples of student who did not follow his, such as, M.

Which students are privileged by this definition of the good student?
Students who follow direction well, and do not question authority or subject matter. These are 'good students', not students who learn 'differently' that traditional education. There are many factors as to why students may not 'sit and behave' in the traditional sense, could be as simple as they are not getting fed a proper breakfast. Therefor only a small group of people are privileged 'good students' by this understanding of a 'good student'.
What is made impossible to see/understand/believe because of these commonsense ideas?
People who are 'good students' may find it difficult to see and understand those who learn differently than the traditional system. They may quickly see these students as 'bad' or troublesome rather than examine, how the student does learn and how and when they best 'behave'. Other teachers may realize the circumstances of a particular student but think that the student needs to adapt to be a good citizen. Rather than, adjusted their classroom so that the student can enjoy learning, subjects, and work with the student so that they can learn methods that work for them. Without examining the students we can quickly come to the commonsense- this student doesnt listen, or follow direction, they are not a good student, they should be disciplined so that they can learn to be a better student. Being a 'good student' often heavily relies on being a 'good teacher' and finding ways to stimulate your students in a way they learn. 
Kumashiro (2010). Against Common Sense, Chapter 2 (pp. 19 – 33) – “Preparing Teachers for Crisis: What It Means to Be a Student”