These four coaching moves aren't quite rocket science. The only research I did in finding these is in watching good teachers and coaches, trying out some of their moves, and thinking to situations in which I've been coached myself. These moves will work with both students and teachers that you coach. I hope they're helpful.
This also happens in reading when we teach into a new skill that seems difficult. Let's take theorizing. When introducing the idea of theorizing in a certain way in a book, this can be challenging for a student, especially if the text is complex. You can take away some of the heavy lifting caused by the complexity of the text if you try the skill out in an easier text. Things can seem so much clearer when the context is easy. The secret is then going right back into the more difficult (actually, just right) text and trying out the new work while it's fresh in their minds.
It's for this reason in writing that we make distinctions between the content and the structure. We teach personal narrative before teaching more complex kinds of narrative writing including fiction and fairy tales. We want kids to become better at narrative structure in a familiar context (themselves) before having them invent a whole new reality. We want kids to write essays about a familiar topic before introducing an essay that is research-based. We (well, I) needed to learn to drive automatic before delving into a stick shift. (I'll let you know when I get there!)
We do this with our kids, too. However, so much of the work they need to do when they read and write is invisible. We have to work to somehow make it visible by naming the mental act of what they do. The easier the task seems to us, the more difficult it is to break it down, because we can do these things with automaticity. For example, in writing, we might feel tempted to say something like, "add dialogue." That's an assignment, because we didn't effectively teach them how to do that. We just told them to do it. We have to break it down more, especially if kids are struggling with it. "Picture your character and think about what he's feeling. Think of what he wants his friend to know. Say the words that would make him get his point across. Now say them again with the feeling he's having." This is much more precise coaching that breaks the steps down to exactly how to write the dialogue in a stronger way than the student could have done on his or her own.
In minilessons, we start by teaching (usually through demonstration...all the teacher), then go to active involvement (kids, often with partners in a controlled context), and then allow kids to try the work on their own (in independent practice). We provide some of the heavy lifting in reading by teaching certain skills first in read aloud, shared reading, or guided reading. We provide some of the heavy lifting in writing by teaching skills in interactive writing. In coaching types of conferences, we actually go back and forth with students as they try something out together with us. It's the art of gradual release of control that makes kids more successful without becoming too dependent on their partners or their teachers.
Sometimes the metaphor can be a slogan. In order to get students to write with greater focus we say things like, "Write like a mitten and not like a glove. When you write like a glove, you say a little bit about this and this and this (pointing to each finger). When you write like a mitten, you talk a lot about one thing (pointing to the palm and fingers all together)." We talk about watermelon and seed ideas. We use physical representations about the invisible aspects of learning all the time.
Sometimes the metaphor is a mnemonic device that helps you remember the steps of a multi-step strategy. Does McDonald's sell cheeseburgers (long division). All good boys deserve fudge (musical notes).
Sometimes the metaphor is an object that reminds students of how to do something. A good story can go a long way with these metaphors. You might tell a story about running out of gas one day, and then relate it to strengthening your stamina in reading, writing, talking, or doing anything for sustained periods of time. This gas tank or car can be there as a permanent reminder of strategies you've taught related to it.
The greatest kinds of images are usually out-of-context ones. Relating something that isn't school-related to something we learn in school helps kids remember it more vividly.