Time is winding down, you have maybe 1 minute left, people in the class are shuffling and you're losing their attention -- they're thinking about where they need to go next. You finish off your thought from that part of your outline, ask "Any questions?" and give it 1 second. (You actually aren't expecting any questions, and secretly know that peer pressure of a group makes that very unlikely!) Then you say, "OK, let's pray" and say a short appropriate prayer that is your official close.
Teachers often miss the opportunity to end classes and Bible study times with a strong "launch."