Probably the single thing I like to do most in my job is co-teach. It's fun, it's powerful, and the kids get a great perspective from seeing it. Typical teaching involves one person who is either distributing the information or a chief facilitator of kids finding that knowledge. To put it simply, the kids in the classroom learn while the teacher teaches. When you co-teach it divides not just the load, but it also mixes up the roles in the classroom a little bit.
We often ask kids to participate in group work, because collaboration is an important skill. Yet, they don't get to see any of the collaboration we do as teachers. They have no model for how a pair should work together. When kids watch two teachers working in tandem it can lead to some great learned behaviors about working with a partnership. They also get to observe teachers learning from each other. Often co-teaching can lead to aha moments from one teacher to another. Phrases like "I'm glad Mrs. ______ shared that example, because I haven't thought of it like that" are great for kids to hear.
Watching two adults work together, learn from each other, and have professional dialogue is something our kids need. I'd argue that we need to teach collaboration and allow opportunities for it to happen among our students, but we as teachers also need to participate in it so our kids can see what it looks like in action.
Instructional Technology Coach