In this stanza, the effect of characterizing black teenagers as both "thugs" and "dark delinquents" and "college-bound" students eager to learn is to create an impactful contrast between perception and reality. The speaker is pointing out that the people in this gang are often judged and labeled based on negative stereotypes, even though some of them are college-bound and interested in learning. This contrast highlights the gap between how these young people are often perceived and the reality of their lives and goals. It suggests that people's perceptions of others can be based on incomplete or biased information, rather than a true understanding of who they are and what they are capable of.