Lesson objective: Solve word problems that involve the addition of three addends by grouping known facts such as tens or doubles to help solve problems more efficiently.
This lesson helps to build fluency with addition of three addends. A ten frame is used here because it supports the concept of making a ten. This work develops students' understanding that when we are adding numbers, it doesn't matter how they are grouped..
Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they analyze word problems for important information to help them understand the question and find a solution. Students also engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they use facts they already know in order to make adding three numbers more efficient.
Key vocabulary:

addend: one of the numbers in an indicated sum of two or more numbers (e.g., 4 + 3 + 1 = 8; 4, 3, and 1 are addends)

double fact: an addition equation in which each addend is the same

equation: a mathematical sentence stating that two expressions are equal

group: a number of people or objects that are assembled together or that have some unifying relationship

known fact: an equation that can be automatically and correctly stated without counting

sum: the result when two or more quantities are added

ten fact: an addition equation with two addends that total or equal ten
Special materials needed:
 double ten frames
 multicolored counters