What is the effect of the repetition of the word "we" in the speech

Parallelism is an especially effective technique to provide structure, order, and balance in your speech, in addition to clarifying your argument. Repetition also helps emphasize your point to your directly to your audience. The audience is more likely to remember something that has been repeated.

The effect the repetition of the word "we" throughout the poem shows off the group and the peer pressure side of things. The poem says" We real cool." This proves further to the point that the group is doing to be cool in front of their peers more or less peer pressure.  One person would not be logical to do this stuff mentioned in the poem so the constant we is to send the message of the group affecting each other.