In what ways is K-12 tenure different from tenure at the university level?

Tenure comes from the Latin word tenere, which means to hold or to keep. Tenure looks different in every state at the K-12 level. I will give you a brief history of tenure, an explanation of what it consists of at the university level, an overview of the controversy surrounding it, and my own experience with tenure as a K-12 teacher in Kansas. 
Tenure had its beginnings in this country when ten thousand teachers came together in Chicago for the first meeting of the National Education Association, the largest labor union in the United States. New Jersey was the first state to pass "fair dismissal rights" in 1909. In the late 19th century and early 20th century, teachers could be fired for any reason, including unpopular political views. Women were often fired for becoming pregnant, or even for wearing pants. By the late 1950's, eighty percent of all K-12 teachers in the United States were tenured. 
At the university level, tenure is a permanent teaching contract. Professors can enter "tenure-track" positions, and it takes at least seven years to achieve tenure. Most professors are required to obtain the highest level of degree in their field (usually a Ph.D.) and to publish numerous research articles in professional journals. Many "tenure-track" positions are competitive, meaning it is possible that more professors are hired than there are positions to be filled. Once a candidate has been given tenure, they are able to hold that position for life. In 1996, Congress abolished the mandatory retirement age for several positions, including professors. Tenure is important at the university level to protect academic freedom.
Recently, there has been a lot of controversy surrounding the idea of tenure. Opponents say it causes teachers to become complacent and lazy. It causes teachers to put in minimum effort, rather than going above and beyond as they would in a merit-pay system. Others say it makes it too difficult to remove incompetent teachers. Michelle Rhee, former chancellor of Washington, D.C. public schools, has been an outspoken advocate for the abolition of tenure. Some say the process of firing a teacher who has been given tenure is so difficult and costly, that many ineffective teachers simply get passed around to other schools. Former California Governor Arnold Schwarzenegger called this "The dance of the lemons." Another argument is that tenure has outlived its necessity. They argue that due to collective bargaining, state and federal laws protecting workers, and job protections through court rulings, or precedents, tenure is no longer needed. 
I am a public school teacher in Kansas. I have a continuing contract, which I received after three years of favorable evaluations. This means that if I am non-renewed or if my supervisor recommends dismissal, I have due-process rights. This means I can appeal the decision. This doesn't mean I will be successful in that endeavor, just that I have a right to do so. I am still evaluated every three years using Charlotte Danielson's Framework for Teaching. I am evaluated on four domains: planning and preparation, classroom environment, instruction, and professional responsibilities. Each domain is quite extensive, and expectations are high. If I receive an unsatisfactory evaluation, I will be put on a growth plan, known as being placed "on improvement." If I don't demonstrate growth in the areas identified, I can be recommended for non-renewal or dismissal. The board of education would have to approve it, as they approve all hiring, firings, and separations. They usually side with the recommendation of the immediate supervisor.  
Academic freedom is not as important for me as it is for a professor. I am expected to teach the Common Core State Standards. I am expected to teach the curriculum adopted by the district. No Child Left Behind legislation erased most K-12 academic freedom with its focus on standardized tests.
http://content.time.com/time/nation/article/0,8599,1859505,00.html

https://www.insidehighered.com/views/2010/12/21/defining-academic-freedom