In curriculum and instructional design, think of a “Big Idea” as the “big picture” of what students need to know about. What’s the main point, or what is the most important thing that students should understand years later?
Big Ideas are, themselves, timeless. How one works with an idea might change, but the idea itself remains. For example, the “Writing Process” is a big idea, but what is considered to be good writing can itself change over time or depending upon the particular scenario. Have you ever witnessed self-appointed Grammar Police argue over details such as whether a contraction should or shouldn’t be used in a sentence? Or how about starting a sentence with a coordinating conjunction? No matter the current opinion regarding these details, the writer still goes through the Writing Process to craft and refine the writing to meet the purpose and audience for that particular work.
The Scientific Method is another process that can serve as a Big Idea; the specific area of science is not as important is the student’s ability to work through the process to observe, hypothesis, evaluate, and theorize about those concepts.