Provide a consistent teaching style and content mix. Brain research has shown that humans do not remember facts. Given this data, it becomes clear why the mind tends to compartmentalize information presented in different books, or even different chapters. Providing the necessary background for the teacher is an interesting demand. To learn something new, begin in your own backyard, proceeding from the known to the nearest unknown.
Students come to the class with a widely disparate knowledge base.
ESL students even have a language problem. It becomes important that the lesson series establishes a reference base that is known by all of the students prior to starting. Demanding two years of college science classes as an additional requirement is meaningless. Nuclear Physicists are not prepared to teach high school biology, but we want the elementary teacher to teach and link Physical, Earth, and Life Science information using hands-on science. Background support in the teacher's manual is the only acceptable answer.