The book challenges the model of learning where a teacher carefully crafts a syllabus of topics which, lectured on & tested on, will result in new skills or knowledge for the learner. Instead, it recommends giving learners:

Participation. Actually doing the skill or exercising the knowledge.

Legitimate. Do the real thing, not some safely bowdlerized version of the thing.

Peripheral. Don’t make the learner solely responsible. No “throwing in the deep end” sink or swim. Someone already skilled or knowledgeable is there doing the thing. The learner is helping.

Legitimate peripheral participation rests on the assumption that part of what the learner gains while learning is the skill or knowledge, but part of what the learner gains is confidence. If all you’ve ever worked on are toy problems, you’re still not sure (well, you shouldn’t be sure) that you can operate when faced with a messy, real situation.

Another assumption is that being exposed to expert performance accelerates learning, even when the learner can’t yet appreciate all the subtlety or nuance going on. Mulling over, “Now why did they do that?” late at night is fertile ground for learning.