A teacher is a coach. This overused statement is tired but true. Teachers give students strategies to learn, coach how to learn, and allow students to get into the game by helping them develop their skills. A good coach doesn't always see the limitations of players but rather creates a game plan that accentuates their skills to lead them to success. In the same way, a good teacher coaches kids to use the skills they have to win at learning. No one likes to always lose, yet some of our students do just that every day in school. They never experience the "thrill of victory" (mastering a skill) only the "agony of defeat." Good coaches know how to bring out the strengths of their players and know how to set their players up for victories. Teachers, who are strong in their craft, do the same for students.
Another term that came to mind was a teacher is a juggler. Look in any classroom of good teachers and you'll see multiple things going on one after the other. Yes, there are planned lessons that teachers follow, but what about the days when real learning is taking place that's not in the lesson plan? A discussion develops that leads to a plan of action by students which they implement. Teachers have to be able to keep one thing in the air while knowing how to toss the rest of their day in such a way that reflects authentic learning. Jugglers were the court jesters in days gone by so they needed a strong sense of humor to keep everyone happy. Not much has changed today. Good teachers have the ability to laugh at themselves and keep their sense of humor even in the most tense situations.
So there are my three metaphors for the prompt "A teacher is..." Sports has always had a special place in my heart, so for me, I choose to be a coach. A nice balance between instruction and encouragement while helping students to develop their game plan in life. Coaches probably had the biggest impact on my life, setting an example for how to be effective in this role. So find a metaphor for a teacher, think about it and write about it. Then be that metaphor for your students. You never know, it could make all the difference.