Otherwise, new singers may be intimidated, believing that they are the only ones who don't know the song. Give the composer and your group the benefit of learning the music as the composer intended it to be. Review the song. As you finish teaching a song, review it and then come back to it near the end of the session. Unless a group is extremely good or the sing turns out to be extremely popular, don't end the session with a newly-taught work.
Teaching is the central core of the songleader's job.
If you do it well, with enthusiasm and care, you will have great success.