An example of K-6 is the grade range in an elementary school where the child studies the core subjects of reading, language arts, math, science and social studies.
Language arts include reading and writing, along with other related subjects, like spelling, punctuation, and grammar. It basically includes all things involved in literacy.
Math starts with recognition of numbers and what they stand for and goes all the way to simple algebra and geometry.
Science is the study of the natural world, so it starts with classifying leaves and observing rocks in kindergarten, to simple chemistry, and biology. The scientific method is reinforced with science fairs.
Social studies start with family and community interactions, and develop into the study of history, economics, geography, politics, and anthropology.
Additional classes include art, music, computers and keyboarding, and physical education (PE).