Enjambment in this poem helps reinforce the meaning, because it puts the most emphasis on the word "we". It makes the reader really have to think about the "we" that the poem is about.
Rhyme is automatic when the same word is repeated at the end of each line (we), but there is also internal rhyme. This helps force the rhythm, because the rhyming words "cool" "school" "late" "straight" "sin" "gin" "June" "soon" are all very quick rhymes, so you read through the line fast and then linger a second longer on the "we" at the end, pausing to move to the next line. Again, it just puts more emphasis on the "we" so that the boys are the absolute focus of the poem.