Before You Begin this Unit… 

Unit at a Glance 
Consider that you have been working with the students on addition during unit 1 and 2. You will want to have data that shows how students are progressing in their fluency with addition combinations up to 10+10. As mentioned in unit 1 students should be exiting grade 2 with mastery of most combinations up to 10+10. This unit assumes that students are fluent with these facts. Those who are not fluent are in need of intervention. This is the 2^{nd} of 3 units in grade 3 on addition and subtraction, which can really help you to make instructional adjustments as you work with students. Some may be using numbers, strategies and ideas from the previous unit, while data supports others moving onto activities and experiences that are offered in later investigations or even unit 3.
Remember that your students may come with a traditional algorithm as their primary strategy for adding and subtracting. Your goal in grade 3 is fluency (accuracy, flexibility and efficiency). The algorithm should be celebrated for what it reveals about the child’s fluency (accuracy and efficiency). Students must also reach flexibility, which is not simply being able to solve a problem in a different way. It involves making choices about the strategy to use to be most efficient depending on the numbers provided. When students use only one strategy for every set of numbers or situation they are showing us that they are no longer paying attention to critical elements of the numbers. This practice causes issues in grades 4 and 5 when students need to draw upon this number sense to add and subtract fractions. 
Suggested Dates: Estimated Duration: 26 lessons Investigation 1: 7 lessons (include session 1.7A) Investigation 2: 7 lessons Investigation 3: 6 lessons (skip session 3.1) Investigation 4: 6 lessons 

Standards Addressed in the Unit  
3.OA.8 Solve twostep word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding.
3.OA.9 Identify arithmetic patterns (including patterns in the addition table or multiplication table), and explain them using properties of operations.
3.NBT.1 Use place value understanding to round whole numbers to the nearest 10 or 100.
3.NBT.2 Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction. Link to CCSS Unpacking DocumentUpdated Sept. '15 