Tests were given to a nine-year-old boy to establish the constraints operating when he was writing poetry. The tests involved writing cloze tests on poems by poet Ted Hughes and on a poem the boy had written a year earlier. The boy was also asked to write a poem and then to discuss what he was thinking as he wrote. The following constraints were identified as operating during his poetry writing: (1) the subject must be exciting, (2) words must be more carefully chosen than in prose, (3) some details are inappropriate for poetry, (4) words must be vivid but not too vivid, (5) some syntax is inappropriate for poetry, and (6) the poetic line is significant. The interview showed that when writing, the boy generally had a vivid mental image to which he tried to match appropriate vocabulary. Some words he struggled for, but some metaphors came easily and without self-consciousness. In a few cases he seemed unaware of the startling appropriateness of his imagery. Thus, the boy was aware of the poem as a type of writing with special constraints that encouraged him to express experiences with controlled vividness. He appeared to be very conscious of his overall purpose even though some of his most vivid imagery was presented unselfconsciously. (Author/HTH)