Deschooling is a term used by both education philosophers and proponents of alternative education and/or homeschooling, though it refers to different things in each context. It was popularized by Ivan Illich in his 1971 book Deschooling Society.
Philosophically, it refers to the belief that schools and other learning institutions are incapable of providing the best possible education for some or most individuals. Some extend this concept beyond the individual and call for an end to schools in general. This is based on the belief that most people learn better by themselves, outside of an institutional environment, at a self-determined pace. This is the meaning of the term as used by Illich.
Another common criticism is that institutionalized schooling is used as a tool for the engineering of an ignorant, conformist working class through constant schedules and prearranged time blocks and one-size-fits-all teaching methods.
In a practical context, it refers to the mental process a person goes through after being removed from a formal schooling environment, when the "school mindset" is eroded over time. Deschooling may refer to the time period it takes for children removed from school to adjust to learning in an unstructured environment.
Families who have taken their children out of school to homeschool often find their children (and often the parents too) need a period of adjustment - learning to live without the reinforcement of grading and regimented learning. It is typically used to describe children who have been removed from school for the purpose of self-directed homeschooling, but technically applies any person leaving school, either by dropping out or graduating.
The term is used by some as a synonym for unschooling, but others make a clear distinction. Some proponents of the theory, or parts of the theory, include John Holt, John Taylor Gatto, Neil Postman, Paul Goodman, George Dennison, Richard Farson, and others.