In the United States, kindergarten is usually part of the K-12 educational system. While kindergarten was once viewed as a separate part of the elementary program, it is now generally considered the first year of formal education and fully integrated into the school system.[26] In most state and private schools, children begin kindergarten at age 5 to 6 and attend for one year. Though in many states kindergarten is compulsory, as the age of required schooling begins at age 5, in others, compulsory education begins at age 6, 7 or (in two states) 8. 43 states require their school districts to offer a kindergarten year.

K = kindergarten

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Note added at 12 mins (2013-12-30 16:52:35 GMT)
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http://en.wikipedia.org/wiki/Kindergarten#United_States


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Note added at 19 hrs (2013-12-31 12:19:30 GMT)
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Regarding "unit," it can be added to kindergarten to make it a separate physical structure or an organizational structure within this particular school system. I used kindergarten as a general school division.

So, YES, "kindergarten unit" completes the answer.