The English used in this article may not be easy for everybody to understand. (October 2011)
A lesson in school is a planned period of time for learning. It involves one or more students being taught by a teacher. A lesson may be either one section of a textbook or a short period of time during which learners are taught about a subject or taught how to perform an activity. Lessons are generally taught in a classroom but may instead take place in a situated learning environment.
Also, a lesson also means a learner learning something he did not know before. Such a lesson can be either planned or accidental, enjoyable or painful. The slang phrase "to teach someone a lesson", means to punish or scold a person for a mistake they have made making sure that he does not make the same mistake again.