Math Windows: Subtraction includes five 8 1/2 x 11 inch double sided write-on/wipe-off cards. 3-hole punch binder system for easy storage in any classroom, daycare or preschool setting. Larger windows for easier writing for younger students. Math windows provide self-checking system for easy learning by single students. Subtraction set contains subtraction facts 0-12 and mixed review. Great for students in grades 1-5.