Jack
Jack is the protagonist of the book as well as its first-person narrator. That narration takes the unusual form of one-sided discourse with his teacher. The teacher is struggling to get students interested in poetry and the book takes the form of Jack's responses to the unspoken side of this discourse. It is only through Jack's responses to the teacher's engagement that one intuits that side of the discussion.
This structure also impacts how information about Jack is conveyed. For instance, the very first words are Jack complaining that he doesn't want to write poetry because only girls do such a thing. As the book progresses, it is clear that Jack not only can write poetry but is surprisingly creative in doing so.
The title of the book is likewise revealed through the poetry assignments. It is eventually disclosed that Jack once had a pet dog named Sky. He is oddly hesitant to speak of the dog at first and is only moved to do so as the tragic story of Sky becomes fodder for his most sophisticated poem.
Miss Stretchberry
Miss Stretchberry is Jack's teacher, occupying room 105. Because the only communication with her is limited to Jack's perspective, everything that the reader learns is filtered through Jack's limited lens. As a result, she is basically a one-dimensional character occupying the limited space that most students have for viewing their teacher.
What is definitely known is that Miss Stretchberry is a dedicated instructor with a love of literature. It gradually becomes apparent that she also has a good eye for seeing potential in her young students. Her primary role in the story is to push Jack to realize his hidden talent for crafting verse.
Like any especially effective teacher, Miss Stretchberry broadens the horizons of her students by prying open their closed minds. This she does not by forcing her opinion as to what constitutes effective poetry on her students but by exposing them to a wealth of different writers and poetic forms. Jack does not even realize his early communication with his teacher has been poetry until he learns that this form of writing takes on many different styles he never knew existed.
Walter Dean Myers
On March 13, Jack is introduced to the poet who forever changes his life. He tells Miss Stretchberry that the poem she read that day was the best poem ever. This reading introduces the most significant plot twist in the book. Jack becomes so enamored of this real-life poet that he becomes obsessed with inviting Myers to speak to his class.
"Love That Boy" is the poem by Myers that inspires the title of the book. Jack is motivated to write a poem titled "Love That Dog" about the loss of his beloved dog, Sky. Jack copies the style of Myers' to the degree that he fears the poet will accuse him of plagiarism. Jack's homage to his greatest influence is not revealed until the final page.
By this point, Jack has undergone a rollercoaster of anxiety over wondering whether Myers will accept his invitation and actually show up to his class. Myers does show up as a result of being in town to visit a friend. Jack is thrilled by the poet's sincerity and genuine interest in the verse written by his classmates. Jack holds back on his poem until Myers confesses he would be flattered to learn that his words inspired another poem to be written.
