What does Isaac tell the narrator to do in order to differentiate between the rich and poor students at the university in the novel, All Our Names?

In order to tell the rich students from the poor ones at the university, Isaac tells the narrator to look at the students' shoes. The rich students have new or perfect looking shoes while the poor students have badly damaged, dirty, or falling apart shoes. As the narrator and Isaac's shoes are dirty and full of holes, they know that they will not be able to fit in with the rich students.