This unit calls for students to mentally add and subtract multiples of 10 or 100 to any number between 100 and 900. Students apply their skip counting skills to addition and subtraction situations. The ability to skip count by tens or hundreds is critical for mentally adding or subtracting. Skip counting and mentally adding and subtracting tens and hundreds are important skills that will move students toward more sophisticated strategies. Working with place value blocks before moving to mental computation will benefit many students.
Key Concepts:
 We can use skip counting to add or subtract because, when we count, we move along the number line.
Prior Knowledge Needed:
 Unit 1: Understanding ten ones make a ten (1.OA.C.6)
 Unit 11: Adding multiples of ten (1.NBT.C.4) (1.NBT.C.5)
 Unit 14: Using understanding of place value to add and subtract (1.NBT.C.5) (1.NBT.C.6)
 Grade 2 Unit 6: Understanding three digit numbers (2.NBT.A.2)
Units on the Horizon:
 Developing foundations of multiplication: Unit 12 (2.OA.C.4)
 Demonstrating fluency in addition and subtraction: Unit 15 (2.OA.B.2)
 Exploring equal groups as a foundation for multiplication and division: Unit 1 (3.OA.A.1)
Lessons

Lesson objective: Extend understanding that skip counting by tens and hundreds. Students bring prior knowledge of understanding place value in order to add and subtract from 1.NBT.C.5. This prior knowledge is extended to using mental math to add and sub...

Lesson objective: Relate skip counting to using mental math to add ten or one hundred. This lesson helps to build procedural skills with mentally adding ten or one hundred. Hundred charts are used here because they support the mental math that students ...

Lesson objective: Relate skip counting to mental subtraction. Students bring prior knowledge of adding and subtracting multiples of ten from 1.NBT.C.5. This prior knowledge is extended to mentally adding and subtracting by 100 as students work on a task...

Lesson objective: Relate skip counting to mentally subtracting. This lesson helps to build fluency using mental math to subtract by skip counting backwards. Hundreds charts and base ten blocks are used here because they clearly show changes in numbers w...

Lesson objective: Apply skip counting to using mental math to subtract. This lesson provides an opportunity for students to apply their knowledge and understanding to defend their choice of student thinking. Kareem makes a conjecture about skip counting...