One of the first activities that I did with my students that really sh owed me who had good number sense was Close to 100. I did this activity right at the beginning of the year with my fouth graders. All of my students were on task and so it was easy for me to walk around the room and observe. It made me realize not only who could add and subtract, but how well they understood place value as well. I remember seeing a student that was really struggling with the game. This was a huge clue to me that this child was lacking in number sense. I was able to discuss this with the parent right away and have seen improvement at the year goes on. As we have revisited the activity through out the year and added different twists, I was able to see the strategies that some of my students developed and how these strategies were strongly related to their number sense. I haven't tried Close to 1000 yet, but am eager to see how my students adapt.