Kirk was considered to be both a pioneer and leader in the field of special education for over 50 years. He devised tests and wrote prolifically about the early education of children, particularly those with learning disabilities. Kirk was extremely influential in passing federal legislation in the field of special ed.

In 1962, Kirk and five others were sent by John F. Kennedy to the Soviet Union to study their programs for mentally retarded children.

Samuel Kirk reintroduced the term learning disorder in 1963 in an attempt to gain greater popular interest and make parents aware of potential problems within their own children. Kirk's general interest was the early diagnosis and mainstreaming educational efforts for exceptional children, with early intervention paramount to a successful increase in the intelligence of the learning disabled. He was an important figure in the origination of Head Start which serves low income children and their families (children from birth to age five, along with pregnant women).

Besides Project Headstart (1969), Kirk was deeply involved in the Learning Disabilities Act, and later with M. Hammil (1976), in the diagnosis of learning disorders of dyslexic students.

Kirk has maintained that most Learning Disorders have never even been diagnosed. He has argued that once children are examined and found to have one of several learning disorders, they should (as much as is possible) be mainstreamed with "normal" students. In this, Kirk has in general, received support from the parents of children with learning disabilities, support from educational philosophy, but has been attacked by many individual teachers who resent the greater demands made by the inclusion of learning disabled children into their particular classrooms.

Over the years, Samuel Kirk has seen Head Start grow from a set of simple services into (in some cases) an elaborate set of activities which include dentistry, health, and free meals for certain disadvantaged children.