This product provides a fun way to access your students' basic number sense. It includes place value, estimation, addition, and subtraction problems. Most of the work focuses on three digit numbers, but a few four digit numbers are included to challenge students. As the students complete each worksheet, they proceed to the next level in Number Ninja training. The Number Ninja Challenge is designed to assess individual student mastery AFTER the concepts have been taught or as a small group activity for reteach purposes with struggling students.