The main focus of educational interest and research at that time was the question of how best to produce obedient soldiers who would uncritically follow orders in battle, so Neill's ideas, which tried to help children achieve self-determination and encouraged critical thinking rather than blind obedience, were seen as backward, radical, or at best, controversial.
Many of Neill's ideas are widely accepted today, although there are still many more "traditional" thinkers within the educational establishment who regard Neill's ideas as threatening the existing social order, and therefore controversial.
Neill founded Summerhill School to demonstrate his educational theories in practice. These included a belief that children learn better when they are not compelled to attend lessons. The school is also managed democratically, with regular meetings to determine school rules. Pupils have equal voting rights with school staff.
Neill's Summerhill School experience demonstrated that, free from the coercion of traditional schools, students tended to respond by developing self-motivation, rather than self-indulgence. Externally imposed discipline, Neill felt, actually prevented internal, self-discipline from developing. He therefore considered that children who attended Summerhill were likely to emerge with better-developed critical thinking skills and greater self-discipline than children educated in compulsion-based schools.
These tendencies were perhaps all the more remarkable considering that the children accepted by Summerhill were often from problematic backgrounds, where parental conflict or neglect had resulted in children arriving in a particularly unhappy state of mind. The therapeutic value of Summerhill's environment was demonstrated by the improvement of many children who had been rejected by conventional schools, yet flourished at Summerhill.
Strongly influenced by the contemporary work of Sigmund Freud and Wilhelm Reich, Neill was opposed to sexual repression and the imposition of the strict Victorian values of his childhood era. He stated clearly that to be anti-sex was to be anti-life. Naturally, these views made him unpopular with many establishment figures of the time.
Neill also had special "private lessons" with pupils, which included discussions of personal issues and amounted to a form of psychotherapy. He later abandoned these "PLs", finding that children who did not have PLs were still cured of delinquent behaviour; he therefore concluded that freedom was the cure, not psychotherapy.
During his teaching career he wrote dozens of books, including the "Dominie" (Scottish word for teacher) series, beginning with A Dominie's Log (1916). His most influential book was Summerhill: A Radical Approach to Child Rearing (1960) which created a storm in U.S. educational circles. His last work was his autobiography, Neill, Neill, Orange Peel! (1973) He also wrote humorous books for children, like The Last Man Alive (1939).
A. S. Neill was married twice; his second wife Ena Wood Neill administered Summerhill school with him for many decades until their daughter, Zoe Readhead, took over the school as headmistress.
Another major contributor to the field of Libertarian Education was Bertrand Russell whose own self-founded Beacon Hill School (England) (one of several schools bearing this name) is often compared with Summerhill. Russell was a correspondent of Neill and offered his support.
Such critics often focused on what they (falsely) claimed to be the laxness of sexual morality at Summerhill.
Modern advocates, such as John Taylor Gatto, John Holt and many others in the unschooling movement, democratic school movement, free school movement and homeschooling movements, have taken Neill's ideas further and updated them, providing energetic and radical critiques of the compulsion-based schooling which is still prevalent in most countries.
Due to the continuing international corporate demand for employees who can think critically and be self-motivated, as well as to the growing demand from parents for a system of education which reflects their ambitions for their children, compulsion-based systems in many countries are now gradually being reformed along much the same lines that Neill recommended.
Summerhill School, which Neill founded, has recently (2007) been accepted by the UK educational establishment, in particular OFSTED, as providing a good quality of academic education for children. Summerhill has also been recognised by the United Nations for its exceptionally good treatment of children.
"The convention of the Rights of the Child makes particular reference to children's rights to participate in decisions affecting them and Summerhill, through its very approach to education, embodies this right in a way that surpasses expectation." - Paulo David, Secretary, UN Committee on the Rights of the Child
A.S. Neill sat for sculptor Alan Thornhill for a portrait in clay. The correspondence file relating to the A.S. Neill portrait sculpture is held in the archive of the Henry Moore Foundation's Henry Moore Institute in Leeds and the terracotta remains in the collection of the artist. Bronzes are in the public collections of The College of Orgonomy, New York and the Scottish National Portrait Gallery, Edinburgh (collection reference PG2204).