This is a Smartboard lesson that allows students to practice subtracting numbers within 20. Each page has objects on the page to give a visual representation of the problem. When touched, each object will disappear showing the students the correct answer. On each page students are asked to come up with the correct number sentence to represent the problem and the correct answer. The answers are provided on each page. The preview file has thumbnail shots of many of the pages in this file. The last page can be used for guided practice.