When I was about 12 years old, my parents took my brother and I to see Stevie Wonder in concert. It was my first real concert experience and most of it is now a blur. But 25 years later, the one thing that sticks out in my mind turns out to be something that had nothing to do with Stevie Wonder's music. It had to do with a lady in the front row who couldn't carry a tune if it were strapped to her back.
About half way through the concert, Stevie (or is it Mr. Wonder?) interacts with the crowd and decides to hold a singing contest. He gets three volunteers from the crowd and they each get a turn singing Satisfaction by the Rolling Stones. The winner gets to sing the song of his choice with Stevie Wonder himself. Talk about the opportunity of a lifetime.
Two of the three could sing very well, but I don't really remember much about their performances. However, the third contestant was very sharp. So much so, that even my untrained ear could tell that this lady couldn't sing. Here is the impressive part: in the middle of her singing, Stevie Wonder stops the band and has them adjust the key of the music to fit her voice. He recognized the exact key in which she was singing and made the adjustment to fit her. It did't work--she still stunk, but that isn't the point.
As teachers, we need to do the exact same thing every day. No matter how well we construct a lesson, we need to be ready to adjust to the kid who continues to sing off key. You can't plan for that. The band didn't practice the song in every possible key just in case they had someone who couldn't sing with them. They knew their song, they understood the progression and understood what to do if they started somewhere different than where they had planned.
I believe that an effective teacher is going to be the one who can recognize where a student is in relation to where the objective is, meet him where he is and adjust the plan accordingly. It's not so much about having a great engaging plan all the time. We can plan a symphonic lesson plan in which all the small parts fit together into a wonderful investigation or lecture. But it's what we do when the kid playing the oboe doesn't hear what everyone else hears and plays the wrong notes that really matters.