Kindergartens were introduced by German early childhood educator Friedrich Wilhelm Froebel in 1837. Froebel envisioned his kindergarten—in literal English, "children's garden"—as a space where children, ages four to six, would be sheltered from the outside world, yet nurtured through a combination of play, games, toys, and socialization.
Despite its early implementation, however, kindergarten did not readily become a requirement across the nation. For example, the state of Mississippi did not offer public kindergarten until 1986, and it is still only mandatory in some U.S. States. Also, while full-day kindergarten is the norm in some districts, it is not uncommon to see certain districts offer kindergarten solely on a half-day basis.
Research strongly suggests, however, that the long-term benefits of mandatory full-day kindergarten are worth the investment. The National Education Association emphasizes that studies consistently show that students enrolled in full-day kindergarten programs display significantly higher levels of math and reading readiness than students enrolled in half-day programs or not enrolled at all.
Source:- http://tobecomeateacher.org/how-to-become-a-kindergarten-teacher/