"I am the master of that which I can explain." Writing is an activity that requires deep thought. It can also be a vehicle through which students can build a deeper understanding of subject matter. Sometimes called "writing for understanding," the main focus is not on the correct spelling, punctuation, and grammar, but rather on making sense of the material and communicating it to a specific audience. Not all writing activities involve students with understanding. Taking notes can merely be a rote activity where students just jot down information and do not begin to process it. Writing for deeper thinking involves students in making connections among disconnected ideas, discerning relationships, connecting information to what is already known, and forming opinions about the material. See the Writing Across the Curriculum link at the bottom of the page for more ideas.
Websites on Writing for Thinking:
Why Should I Use Writing Assignments in My Teaching?