Math: Adding and Subtracting Within 20

First graders recently began a new math unit focused on adding and subtracting within 20. Learning goals include applying the properties of operations and using the relationship between and subtraction as a strategy for solving problems. As a foundational understanding of place value and our base 10 number system, students are exploring unitizing, the idea that 10 ones as a unit is called "a ten". They will grow their knowledge of teen numbers as 10 + some number of ones and use this knowledge to add and subtract. First graders will continue solving story problems throughout the unit and learn two new problem types--Add To, Start Unknown ( ____ + 3 = 13) and Take From, Change Unknown (13 - ____ = 10).