At some point in the novel-writing process, I found myself staring at a line of dialogue, asking, "Should she say gonna or going to?" That led to more questions: Do all the characters say gonna or going to? What about the first-person narration? What about wanna and want to?
So I made a list. Under want to and going to, I listed most (but not all) of the adult characters, as well as a child character who's probably not up on the latest slang. Wanna and gonna were for everyone else.
This morning, my friend ctrl+f and I sought out all examples of such language with the intention of making them abide by these rules. And I found that they don't work. Emotions make a difference. Who the listener is and what the speaker thinks of the listener makes a difference. A character who gets excited easily is not going to slow down and say to a perceived new friend, "What are we going to do at recess?"
This novel is not gonna keep to the list.