I've been teaching Sunday School at my church since I was in high-school in the late nineties.
My church, actually our national church, is one of many sponsors of a great resource for religious education teachers, and Christians in general. Opening Doors to Discipleship.
The sponsors are all reformed tradition churches throughout North America:
Opening Doors to Discipleship, teacher training online, is sponsored by five denominations:
Is yours included?
There are four courses:
I've taken the teaching class, and plan to follow up with more when I have time.
I think these courses are definitely designed to be done with at least one other person, but I did them by myself. I know you'd get more out of the lessons if you had some discussion as expected in the units.
I got some great ideas for teaching in my class, some of which are just a repackaging of typical school teacher ideas, but put in a Sunday school environment.
If you're a member of one of these denominations, I recommend you check out some of these classes, they're free, you just need your denominational login code, which your minister will have access to. Ours was also available on the back of our national magazine a few years ago.