How to teach Doubles Plus One/Minus One effectively to first graders

📚 Understanding Doubles Plus One/Minus One

Doubles plus one (or minus one) strategies leverage a child's knowledge of doubles facts to solve nearby addition problems. If a student knows that $6 + 6 = 12$, then they can quickly solve $6 + 7$ by recognizing that $7$ is just one more than $6$, so the answer must be $12 + 1 = 13$. The same logic applies to subtraction, where knowing $6+6 = 12$ also means $12-6=6$ and $13-6=7$. This is a mental math strategy that builds number sense.

🎯 Objectives

• 🍎 Identify Doubles Facts: 🧠 Students will be able to recall basic doubles facts (e.g., $1 + 1 = 2$, $2 + 2 = 4$, etc.).
• ➕ Apply 'Plus One' Strategy: 🔢 Students will be able to add one to a doubles fact to solve a 'plus one' problem.
• ➖ Apply 'Minus One' Strategy: 🔢 Students will be able to subtract one to a doubles fact to solve a 'minus one' problem.
• 🤝 Explain Reasoning: 🗣️ Students will be able to explain their thinking process when using the 'doubles plus one' or 'doubles minus one' strategy.

✏️ Materials

• Number Flashcards: 🃏 Cards with numbers 1-10.
• Counters: 🔴 Small objects (e.g., cubes, buttons, beads) for visual representation.
• Whiteboard or Chart Paper: 📝 To record doubles facts and examples.
• Worksheets: 📃 Containing 'doubles plus one' and 'doubles minus one' problems.

🔥 Warm-up (5 minutes)

• 🗣️ Doubles Fact Recall: 🧠 Begin by verbally reviewing doubles facts from $1+1$ to $10+10$. Ask students to shout out the answers in unison. For example, “What is 2 + 2?” (Students: “4!”)
• 🖐️ Finger Doubles: 🔢 Use fingers to demonstrate doubles. Hold up 3 fingers on each hand and ask, “What is 3 + 3?” Then, add one more finger on one hand and ask, “Now what is it?”

👩‍🏫 Main Instruction (20 minutes)

• ✍️ Introduce 'Doubles Plus One': ➕ Explain that 'doubles plus one' means taking a doubles fact and adding one more. Write $4 + 4 = 8$ on the board. Then write $4 + 5 = ?$ Explain that $5$ is one more than $4$, so the answer is $8 + 1 = 9$.
• 🔴 Visual Representation: 👀 Use counters to demonstrate. Show 4 counters in one group and 4 in another. Combine them to show 8. Then add one more counter to one group to show 9.
• 🗣️ Think Aloud: 💡 Verbalize your thought process: “I know that $5 + 5 = 10$. So, $5 + 6$ is just one more than $10$. $10 + 1 = 11$. So, $5 + 6 = 11$.”
• ✍️ Introduce 'Doubles Minus One': ➖ Explain that 'doubles minus one' means taking a doubles fact and subtracting one. Write $7+7=14$ on the board. Then write $7+6=?$ Explain that $6$ is one less than $7$, so the answer is $14 - 1 = 13$.
• 🤝 Partner Practice: 🧑‍🤝‍🧑 Have students work in pairs. One student says a 'doubles plus one' or 'doubles minus one' problem, and the other solves it using the strategy. Then they switch roles.
• 🧮 Guided Practice: 📝 Work through a few examples as a class on the whiteboard. Encourage students to explain their reasoning.

✅ Assessment (10 minutes)

• 📃 Worksheet Activity: ✍️ Distribute a worksheet with a mix of 'doubles plus one' and 'doubles minus one' problems. Have students solve the problems independently.
• 🙋 Observation: 👀 Observe students as they work, noting their strategies and identifying any areas of difficulty. Ask probing questions such as, "How did you figure that out?" or "Can you explain your steps to me?".
• 📊 Exit Tickets: 🎫 Have students complete an exit ticket with one or two 'doubles plus one' or 'doubles minus one' problems to assess their understanding.

➕ Practice Quiz

Solve these problems using the doubles plus one or doubles minus one strategy:

1. $3 + 4 = ?$
2. $6 + 5 = ?$
3. $8 + 9 = ?$
4. $2 + 3 = ?$
5. $7 + 6 = ?$
6. $9 + 8 = ?$
7. $4 + 5 = ?$