Add and Subtract Fluently

Overview

In this 30-minute lesson, students choose a strategy to add or subtract within 20 and determine unknown numbers in equations. Students build on prior work with counting, making ten, decomposing numbers, and related addition and subtraction facts.

Learning intentions

• Students will be able to add and subtract within 20.
• Students will be able to choose a strategy that helps them solve.
• Students will be able to find an unknown number in an equation.
• Students will be able to explain or demonstrate how they solved.

Success criteria

• I can solve addition and subtraction problems within 20 accurately.
• I can choose a strategy, such as counting on, making ten, using a fact family, or using objects.
• I can find the missing number in an equation.
• I can explain or demonstrate my strategy with words, drawings, objects, or a number line.

Curriculum links

• Addition and subtraction within 20, including using counting on, making ten, decomposing numbers, and related facts.
• Finding an unknown whole number in an addition or subtraction equation.
• Representing addition problems with objects, drawings, and equations.
• Explaining mathematical thinking and comparing strategies.

Lesson structure (30 minutes)

1. 0–4 min · Hook and review. Teacher opens with the mystery-number hook slide and displays 8 +? = 13; students use fingers, counters, or mental math to find the missing number and briefly share how they know.

2. 4–9 min · Model strategy choices. Teacher uses the strategy comparison slides to model 7 + 6, demonstrating counting on and making ten, then models 14 - 5 by decomposing to ten. Students show the strategy with counters, a number line, drawings, or equations and identify which strategy seems helpful.

3. 9–13 min · Connect fact families. Teacher displays a fact-family triangle or writes 6, 4, 10 to show 6 + 4 = 10, 4 + 6 = 10, 10 - 6 = 4, and 10 - 4 = 6. Students build the related facts with counters and solve one missing-number example, such as ? - 6 = 4.

4. 13–23 min · Supported practice. Teacher distributes the differentiated strategy practice worksheet and assigns each student an appropriate fact range. Students solve addition, subtraction, and missing-number equations using a strategy mat, counters, connecting cubes, or a number line; the teacher circulates, prompts “What do you know?” and “Which strategy will help?” and records accuracy and independence.

5. 23–27 min · Partner strategy share. Teacher pauses the worksheet and displays the partner discussion prompt. Students pair up, explain one solution, and compare strategies using the stem, “I solved ___ by ___. It worked because ___.” Partners may demonstrate rather than read or write their explanation.

6. 27–30 min · Exit check and close. Teacher displays the exit problem and reflection slide and asks students to solve 15 -? = 9 or an individualized equivalent. Students show the answer and strategy orally, with a drawing, or with manipulatives; teacher briefly revisits the success criteria.

Resources

• the Add and Subtract Fluently slide deck
• the differentiated strategy practice worksheet
• Counters, linking cubes, or two-color chips
• Number lines to 20
• Strategy mats showing counting on, making ten, decomposing, and fact families
• Fact-family triangles or number-bond cards
• Pencils, crayons, and dry-erase boards
• Individual student fact-range cards or teacher-prepared problem lists

Assessment

• During modeling, check whether students connect addition and subtraction facts and can represent an unknown with objects or a drawing.
• During practice, record whether each student solves accurately, selects or follows a strategy, and explains or demonstrates the strategy. Provide fewer problems and more modeling when needed.
• Use the exit problem to identify next steps: fact fluency, strategy selection, equation meaning, or explaining mathematical thinking.

Differentiation

• Support: Use individualized fact ranges, beginning with facts within 5 or 10. Provide counters, number lines, fact-family visuals, partially completed equations, and a strategy mat. Read every direction aloud and allow students to answer orally or point to a model.
• Dyslexia-friendly access: Use a clear sans-serif font, large print, strong spacing, limited problems per page, untimed practice, and uncluttered equations. Keep visual fact families available and avoid requiring students to copy lengthy explanations.
• Communication and sensory needs: Offer quiet work space, brief directions one step at a time, repeated modeling, movement during partner sharing, and response choices such as speaking, drawing, building, or writing.
• Advanced learners: Encourage fluent recall within 20, then ask students to solve the same equation in two ways and compare which strategy is more efficient. Invite them to create an equation with an unknown in a different position and explain why the answer is correct.

Extension

• Students create a set of related fact-family equations using three numbers and challenge a partner to find the unknown.
• Students solve one addition and one subtraction problem mentally, then demonstrate a second strategy and explain which method they prefer.