Benefits of K12 education revolve around helping children to succeed in school through consistenty and persistenty. If a child is content with his or her surroundings and classroom environment, then the conditions for learning are better.
If a child is fortunate to remain in the same school from kindergarten to the 12th grade there can be tremendous benefits of k12 education because of a consistent and trustworthy learning experience. It is more difficult when a child has to move to another city or area, but the fundamentals that are learned, are easily transferred in most cases.
The system that educators have been using for hundreds of years still work. Some things just have to be memorized, some subjects such as math, need lots of homework and practice, and things like music, art and writing all need to have lots of practice sessions in order to master the subject matter.
It is ideal to have students in smaller classes when possible, because students will have more time with teachers that way. A class of 50 plus students is a nightmare for a teacher, because there just is not enough teacher to go around.
As more and more technology enters the playing field, the role of the teacher can be supplemented by this technology. Several students can go to a work station together and have separate modules and be self-taught with the teacher watching over them, as the computer model walks them through a lesson.
Children start out in the younger grades learning how to spell, read, and learn basics. 2nd trough 4th and fifth grades, the student learns how to become a fairly competent reader and should be able to reason through problems fairly well.
The sixth through the 9th grade is a period where students broaden their horizons and learn more about history, more advanced math, English and social studies. There may be more in the musical and sports areas, too and the student will be more involved socially at these junior high school levels.
The high school years are more developmental years where more flexibility beyond the basic core courses can be allowed. More depth and detail is the name of the game, until when the student is a senior and is getting ready for college.
The better schools will teach the children more about how to do things for themselves, than to always have to have someone do it for them. The child can learn to look things up on their own and do some serious research on some fairly hefty projects even in the grade school years.
The benefits of K12 education as we know it in this country are a child that knows how to read, write, spell things, and organize. History and more advanced math may be mixed into the equation as well, but by the time the student finishes the 12th grade, it is expected that he or she will be will enough educated that they can either go on to college, or go to work at a starter job. In most cases, the benefits of K12 education have paid off.