There are many use of the literary device diction in this poem. Reason so is that the poem is written in a child's viewpoint, where a child (still in his early years) would have lack the expertise and handiness in his vocabulary and language. Example of use is in the first line 'millionbillionwillion' where it was used by the kid to emphasize the lengthy distance of home to school (yet not having the understanding to express in a grammatically correct way). In line 16, 'lessins' refers to lessons. A similar 'mistake' occurred in line 19; classrooms interpreted as 'glassrooms.' Notions like lessons and classrooms are unfamiliar objects to the child, things that he is unaccustomed to. He might have misheard the words, and that tied in with minor knowledge of the outside world has resulted in misspelt words and.....
Read more:-
http://www.markedbyteachers.com/gcse/english/poem-analysis-the-first-day-at-school-by-roger-mcgough.html
Written by renowned English poet Roger McGough, "First Day of School" epitomizes the innocent ignorance, misunderstandings and insecurities of a child on his or her first day in school, while simultaneously capturing the spirit of childhood innocence and curiosity. The poem has become a beloved looking glass which peers into the mind of a child entering the first stages of the real world. At times, it is confusing and comical, but it also offers a shadow of the childhood wisdom that adults lose sight of in later years.
The poem itself is written in a traditional format, lacking any poetic sophistication or clever techniques. It is almost certainly written this way purposefully, as a child would have no use for such sophistication. There is almost nothing in the poem that could be interpreted as a rhyme either. Rather, it mimics the kind of disjointed observations a child may make when presented with
a new setting. The numerous misspelled words in the poem also serve to contribute to the feeling that this poem is written by a child, who lacks the literary training to know how to spell certain words correctly.
Read more:-
http://www.helium.com/items/2186318-poetry-analysis-first-day-at-school-by-roger-mcgough