Students can apply their knowledge of addition and subtraction to finding the missing part of number models. Provide practice of these skills using these worksheets which range in difficulty. There are dominoes, ten frames, part-part-total diagrams, number bonds and number sentences to help students understand concepts and organize their thinking. Perfect for whole class lessons, extra reinforcement, homework or assessment. After using these worksheets, students will understand the meaning of the equal sign, how to find missing addends and subtrahends, and become more fluent with addition and subtraction within 20.