The birth of the modern theory of adult learning, known as andragogy, occurred in 1946 at a Boston YMCA. A young director of adult education organized a course on astronomy and arranged for a local university professor to teach the class. Although initially enthusiastic, the students quickly became bored with the passive lecture experience and attendance dwindled until the course was finally canceled.

Trying again, the YMCA director rescheduled the course and this time invited a member of the amateur astronomers' club to lead the group of students. As soon as the students arrived for their first class, the new teacher escorted them to the roof of the YMCA and asked them to gaze into the night sky. While they looked up, the teacher asked them what it was they noticed most and what they wanted to learn. Their questions formed the basis for the rest of the course and the teacher led discussions with a telescope on hand for ready use. This experiential method of teaching was popular with the students and the class enrollment swelled.

The young YMCA director, named Malcolm Knowles, took note of the different teaching styles and their dramatically different outcomes. The method of teaching to adult learners' interests and actively engaging the students in their own discovery became the structure Knowles would use for all of the YMCA courses. The astronomy class also marked the beginning of Knowles' lifelong exploration towards understanding adult learning.

Knowles would not adopt the term andragogy until 1970 with the release of his book The Modern Practice of Adult Education: Andragogy vs Pedagogy. Pedagogy, defined as the art and science of teaching, has its word origin in Greek and traditionally has applied to the teaching of children. Knowles' seminal work clearly drew a new distinction between classic methods of pedagogic instruction and adult learning principles.

Knowles' theories of adult learning are complex, but his conclusions can be summarized into four main points:

1. Adults need to know why they are learning something. They should be told how it effects them directly.

2. Adults have a repository of lifetime experiences that should be tapped as a resource for ongoing learning. Similarly, adult learners bring various levels of prior exposure to any topic and that fact should be acknowledged.

3. Adults use a hands-on problem-solving approach to learning. Rote memorization of facts and figures should be avoided.

4. Adults want to apply new knowledge and skills immediately. Retention decreases if the learning is applied only at some future point in time.