A teachable moment is an unplanned opportunity that arises in the classroom where a teacher has an ideal chance to offer insight to his or her students.
A teachable moment is not something that you can plan for; rather, it is a fleeting opportunity that must be sensed and seized by the teacher. Often it will require a brief digression that temporarily sidetracks the original lesson plan so that the teacher can explain a concept that has inadvertently captured the students' collective interest.
Taking this tangent is worthwhile because it is organically timed to maximize impact on the students. Ultimately, the teachable moment could evolve into a full-blown lesson plan or unit of instruction.
During our morning meeting, one student asked why we had Veterans Day off from school yesterday. So, as the teacher, I turned this into a teachable moment to discuss the sacrifices that servicemen and servicewomen have made on behalf of our country, continuing to the present day. The students were paying rapt attention and so we ended up spending 20 minutes discussing our friends and neighbors who are in the military and what it means to our country's future.