John S. Tanner, Notes from an Ameteur: A Disciple’s Life in the Academy (Provo, UT: Religious Studies Center; Salt Lake City: Deseret Book, 2011), 4–6.
A few months ago, I was asked to substitute teach a class. The invitation summoned up early memories, mostly negative, of substitute teachers. Substitute teachers were generally poor stand-ins for regular teachers. They often knew neither the subject nor the students well. Substitutes thus became the butt of class pranks. We would sometimes try to switch names: “My name’s not John but Jim.” Or try to get the substitute to accept ridiculous rules: “Mrs. Anderson always lets us use open book for spelling tests.” Occasionally, of course, a substitute teacher was an improvement on the original and made us dread the day when our regular teacher would return. But this was the exception rather than the rule.
There is, however, another way I sometimes think about substitute teaching. In an essay entitled “We Are All Substitute Teachers,” which appeared long ago in the Instructor, Nan Grass, a former BYU English teacher, asserts, “Every person who is called to be a teacher in The Church of Jesus Christ of Latter-day Saints is a substitute teacher: a substitute for the Savior.”  I like this idea. It has often made me reflect on what kind of a teacher I am when measured against the Master Teacher. A poor substitute no doubt, but better to the degree that I strive to imitate the Master in my own practices.
I believe that all teachers, not just those called to teach in the Church, can properly look to the Savior as a model teacher. Certainly those of us at BYU who try to teach our subjects with the Spirit of God can strive to be substitute teachers, whether we teach statistics or Spanish, genetics or geography, econ or English. For we have taken upon ourselves his name. We have a responsibility to try to (re)present him in our professional as well as our personal lives, a duty to be disciples in our disciplines.
For me this means, among many other things, that I should teach to transform, not just to inform, my students. That I should employ the power of story and analogy and in other ways try to help learners grasp new ideas by using familiar ones. That I should not be afraid to correct in love, nor to set high expectations. That I should always remember the one, even when teaching the multitudes. And, perhaps above all, that I should forget any need to impress and try instead simply to bless.
I was reminded of this last lesson in substitute teaching a few years ago while reading a memoir by Jane Tompkins entitled A Life in School: What the Teacher Learned. In it, Tompkins, a Yale-educated literary critic, tells of an epiphany she had while hurrying to class, late from having stayed up the previous night anxiously trying to prepare what she hoped would be a brilliant lecture. “I was walking down an empty corridor,” she writes,
when I thought to myself for the first time: I have to remember what they want (meaning the students), what they need. . . . As a result of that moment I realized that what I had actually been concerned with was showing the students how smart I was, how knowledgeable I was, how well prepared I was for class. I had been putting on a performance whose true goal was not to help students learn, as I had thought, but to perform before them in such a way that they would have a good opinion of me. 
As an institution, we have received a similar wake-up call reminding us to focus on our students’ performance more than our own. This reminder can be salutary for us as substitute teachers. For surely the Savior in his teaching was fully focused on his hearers’ needs rather than his own. His eye was single to God’s glory and mankind’s good. And he bid his followers to develop this same purity of purpose. His call to have our eyes single echoes still from the Sermon on the Mount off Y Mount, challenging each of us as disciples in the disciplines to become more single-minded substitutes, consumed by love for our subjects, students, and Savior.