You will have noticed that every line ends with er - "order", "wander", "yonder".
There is an internal rhyme too as many words within the lines also end with er or our - “gutter”, “rumour”, “elder”. This serves to increase the pace of the poem.
The very last words of the poem - announcing that Robin is now “the real boy wonder” (line 24) - create the climax of the rhyme scheme.
Armitage also uses very long sentences. There are only five in the whole poem. This also increases the pace of the poem, as we are only allowed short pauses for breath. In addition, it helps to convey the energy Robin has now that he is free of Batman.