Another important way to "sharpen the saw" is to attend a Sunday school workshop or seminar. 
Another important way to "sharpen the saw" is to attend a Sunday school workshop or seminar. A simple online search yields several options of Sunday school workshops. We would also encourage you to contact Herald and Banner Press to see about arranging such a workshop for your church and others in your community. Another option would be to sign up for ministrygrid.com, which provides training of various types for church leaders. A search for ”Sunday school teacher training” on YouTube also surfaces several videos regarding teaching Sunday school. (Note: Be careful in wording your search criteria. Many YouTube videos are not appropriate.) Through iTunes (computer program), several universities offer free courses, which may be of benefit to you.
The advantages of such training, especially in-person events, are obvious: focused training by experts, encouragement from and fellowship with other Sunday school teachers, and the possibility of seeking advice for your specific challenges. Obviously, such training events will require your personal investment. At the least, it will require time and energy. But such workshops may also involve some financial cost.
The question is: are we serious about doing the best for our Master, to the extent that we will reject the status quo and be willing to learn new things, try new methods, and invest in training?