I've been teaching in my church's Saturday theology and Sunday School classes for about a month now and I still can't shake off the feeling of inadequacy. Perhaps this is actually a good thing, as it keeps me begging for fresh supplies of God's grace and enablement every time I wear the teacher's moccasins. I am greatly encouraged (and surprised!) that my pastor is very supportive and has told me that the congregation actually enjoys my Sunday School classes—surprised because I can't see why. I feel that my oral communication sorely needs improvement (I have a stutter), and to hear that the people of my church profit from my blunderings is a great consolation.
Dr. R. Scott Clark told me the following, after I asked for advice following a Sunday School class wherein I particularly felt that I did a poor job: "Teaching requires practice & trust in the Lord's mercy. Real teaching is a dying to self." Needless to say, this was just what the doctor ordered. I realized that teaching is a giving of oneself to the student, done in the spirit of service, with his edification in heart and mind. From then on, I resolved to approach teaching mindful of the fact that I am serving my Lord and tending to His sheep, and performance anxiety introspection is best countered by assuming the humble posture of a servant.
The following article by Sinclair Ferguson, from Themelios (Vol. 36, Issue 2, Aug 2011), although about the preacher and preaching, I believe has wisdom to impart even to the mere teacher: