Activity 2 asks the child to roll 3 dice, count the total number of dots on them, and show that number on the abacus, which has students combine three quantities and represent the sum with manipulatives. The number-specific activity pages (16–20) ask students to draw pictures to show a given number and color abacus beads to represent that number, reinforcing representing totals with drawings and physical models. The sidewalk number line and abacus activities require students to count and combine quantities up to 20.

Students use manipulatives (abacus, base-10 blocks) and drawings (rod and unit cube representations, abacus-style beads) to represent and build numbers 11–20. In the coin activity, students create amounts in multiple ways and are asked to show 17 cents in three different ways, including combinations such as 1 dime, 1 nickel, and 2 pennies (a sum of three whole numbers). Number bond and decomposition activities have students break numbers into parts (e.g., 10 + 5 = 15) using objects and diagrams.

Students create and answer "Do the Math!" cards that use numbers 1–20 and include tasks such as number bonds and counting coin amounts. Students cut, sort, fill in blanks, and make their own cards (30 total), and they answer these cards during gameplay, staying or moving back based on correctness. Example cards prompt students to compute coin totals and identify number bonds, which require performing addition with whole numbers within 20.

In Activity 3, students handle a penny, nickel, and dime and are asked to use the three coins to make different amounts; the text explicitly notes that using all three coins can make 16 cents (10+5+1). Students are asked to show money amounts by drawing coins and to write the resulting number, and they may use an abacus and a laminated number line to count and represent totals. The skip-counting and coin worksheets require students to write amounts (e.g., 13, 14, 16 cents) and to draw coins to represent given totals.

The lesson includes a skills statement that students will "determine the unknown whole number in an addition or subtraction equation relating three whole numbers." Students practice reading and writing addition sentences (for example, reading aloud 5+3=8) and use objects and tools (counters, pennies, and an abacus) to combine groups and find sums. Several activities ask students to create and record number sentences (Animal Addition, Adding on the Abacus, wristband bead counts) and to model addition with counters and the abacus.

Students use play one-dollar bills as counters to add groups of three item quantities (e.g., 2 toy cars + 3 candy bars + 1 coloring book = $6) and write the total on the provided Shopping pages. The materials explicitly tell students that adding three numbers uses the same process as adding two numbers and prompt them to count out and record amounts on a whiteboard or activity page. Activity 2 has students record purchases (draw or write) and compute totals and change using play money, reinforcing addition of multiple addends that sum to less than ten.

Students count pictures in the "What's a Pictograph?" activity where they identify ducks (3), bluebirds (6), and eagles (8) and answer "How many birds did the birdwatcher see in all? (17)." Students also compute a total for the Favorite Foods survey by adding the category counts (3 + 2 + 4 + 6 + 0 = 15). Students create a Skittles pictograph by placing, drawing, and counting candy of different colors, which requires tallying and totaling counts.

Students count and group physical objects (Skittles and toys), record totals, and answer questions such as "How many orange, yellow, and green Skittles did you pick in all?" which requires adding three quantities. Students represent counts with drawings and charts (pictographs and bar graphs) and use those representations to determine combined totals (e.g., "How many games and puzzles do you have altogether?"). The optional Skittles activity has students pick up to 20 Skittles, tally by color, and compute sums from those object-based counts.

Students are asked to use counters, an abacus, and a number line to show adding or subtracting numbers (Activity 1), and are encouraged to draw pictures or write number sentences to solve problems. The "Something's Missing" worksheet has students find unknowns in equations (e.g., 5 + ___ = 10, ___ + 9 = 9) and allows use of manipulatives as needed. The Skills section explicitly lists "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers."

Students make and record addition sentences with three addends using 10 counters in the "Making 10 with Three" activity (e.g., creating groups of 3, 3, and 4 and writing 3 + 3 + 4 = 10). Students use objects and an abacus to model three-number sums in the abacus and the "More Adding Three Numbers" story game (e.g., adding 3 + 4 + 2 to find 9). Students practice matching and computing three-addend expressions on the "Order and Addition" sheet and record sums on student activity pages.

Activity 1 explicitly asks students to add three numbers (examples shown: 4 + 6 + 3 and 5 + 2 + 3) and models looking for pairs that make 5 or 10. The three-dice "Climbing the Path" game has students roll three dice, find the sum of the three rolls, and record/color the matching total. Party Paper Chains and the Wrapping Up "Number Collection" ask students to write addition sentences with three addends (example given: 5+5+5=15), and several activities encourage use of counters, an abacus, or whiteboard drawings to find sums.

The Introduction asks the child to show the number 18 in as many ways as she can and explicitly encourages inclusion of addition sentences with two and three addends and placing coins (or drawings of coins) adding to 18 cents. The materials allow students to use manipulatives (abacus, counters, coins) and drawings to represent and compute number combinations. The Skills list includes "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers," indicating attention to equations that involve three addends.

The lesson's Skills list explicitly includes solving word problems that call for addition of three whole numbers whose sum is less than or equal to 20. In Activity 1 students are asked to create number sentences and solve problems, including a three-addend problem (answer key shows 5 + 8 + 6 = 19). The materials repeatedly prompt students to use objects and tools (counters, abacus, laminated number line, play bills) to find sums and to write number sentences for word problems.

Students are asked to create two addition sentences with three addends where the number is the sum (example given: 2 + 5 + 4 = 11). Students are prompted to use objects and tools (counters, abacus, colorful pictures) and to practice showing the number on the whiteboard, including the prompt "given 11 counters, how might she divide them into 3 groups to create three addends to add up to 11?". The activity includes blanks such as "10 combines with ______ to make the missing number," which students fill in to represent unknown addends.

Students roll three dice, write the three numbers as an addition sentence (e.g., 1+4+6), and use counters, a number line, or an abacus to find and record the sum in Activity 1. The Life Application prompts students to solve contextual kitchen word problems that add three quantities (e.g., 3 plates + 2 bowls + 4 cups) and to lay out items to illustrate the problems. The Skills list explicitly names "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers," indicating attention to three-term equations.