I am a mere student teacher. But, in the school that I am in, two teachers are using the TERC system. One of them happens to be my cooperating teacher. One of the key things about using Investigations is writing. Where I am at, most grading and assessment occurs on two levels. One grade is a concept grade. Did the student correctly perform and understand the concepts that were being taught? The second level is communication in writing. Can the students clearly communicate how they solved the problem. Now, step one is not so bad, but step two is the hardest. The easiest way to do step two, and this is kind of how my teacher has prompted me, was pretend you are one of the lucky people to grade state testing. (I am in Delaware and writing is a major thing in our state tesing). Sure, you know what the children are trying to say, but if this was the state test, could you figure out what the child is saying. Grading an assessment like this helps out because this way, you can explain to the students how you graded, but also prompt them to be excellent writers when writing to explain what they did. Maybe this suggestions helps some teachers!