By the end of 3rd grade students should be able to fluently add and subtract within 1,000 using their knowledge of place value and the properties of operations. Below is a guide and a video about the properties of addition that explain in further detail what your child is learning. Also included are two videos that share a few addition and subtraction strategies that lead to mental math fluency.
Addition & Subtraction Guide
Properties of Addition
Addition Strategies
Subtraction Strategies