Addition and Subtraction to 20
Warm-up
Doubles challenge: teacher says a number 1-10 and students say the double. Then near-doubles: 6+7. Who can explain? I know 6+6=12, so 6+7 is one more: 13. This warm-up activates the doubles strategy before the lesson.
Explore
Stations: (1) Doubles and near-doubles with linking cubes: build double towers, then add one more. (2) Making-10 with ten-frames. (3) Fact families: given one fact, write the other three. Rotate after 5 minutes. Circulate and ask students to explain their reasoning.
Formalize
Debrief the fact family station: write 6+7=13. Ask: what other facts do we know for free? 7+6=13, 13-6=7, 13-7=6. One fact gives four. That is the power of understanding how addition and subtraction are connected.
Addition and Subtraction to 20
Number talk: 14-6. Most students count back; some use the inverse: 6+?=14. Share both approaches. Which is faster? Why? The goal is flexibility: choosing the right strategy for the numbers, not applying one method always.
Practice
Students complete a mixed set of addition and subtraction problems to 20, writing their strategy beside each answer. Exit ticket: 15-7. Students write the answer and the related addition fact they used.
Exit ticket
Students complete a mixed set of addition and subtraction problems to 20, writing their strategy beside each answer. Exit ticket: 15-7. Students write the answer and the related addition fact they used.
Step 1: Ask: "What double is hiding inside 7 + 8?" Students should spot that 8 is just one more than 7, so 7 + 7 is hiding inside.
Step 2: Use the known double: 7 + 7 = 14. (Doubles are usually learned early and feel safe.)
Step 3: Adjust: 8 is one more than 7, so the answer is one more than 14. So 7 + 8 = 15.
On cubes: build two towers of 7 side by side, then snap one extra cube onto one tower. The "double plus the extra one" is visible.
Record the reasoning, not just the answer: 7 + 8 = 7 + 7 + 1 = 14 + 1 = 15.
Way 1 — count back: start at 13, count back 5: 12, 11, 10, 9, 8. Keeping track of five counts on fingers while saying number names backwards is genuinely hard — watch for students who lose count and land on 7 or 9.
Way 2 — think addition: ask "5 plus WHAT makes 13?" Jump 5 → 10 (that's 5) then 10 → 13 (that's 3 more): 8 altogether. Same answer, and it reuses making-10.
Step 3: Let students try both on 14 − 6 and vote for the strategy that felt safer. Most choose think-addition — and that preference is exactly what you want going into Grade 2.
The point to make explicit: subtraction problems can be solved by addition thinking. The two operations are one fact family.
What you see: 9 + 4 is answered confidently; 13 − 4 gets a blank stare — even though it's the same fact family.
Step 1: Diagnose: subtraction taught only as "take away and recount" gives students no way in when the numbers get bigger. The missing link is the part-part-whole relationship.
Step 2: Rebuild with a bar model: draw a whole bar labelled 13, split into a part labelled 4 and a part labelled ?. Ask: "What goes with 4 to make 13?" — the student is now ADDING, which they can do.
Step 3: Connect all four facts of the family explicitly: 9 + 4 = 13, 4 + 9 = 13, 13 − 4 = 9, 13 − 9 = 4. Build one triangle fact card (13 on top, 9 and 4 below) and quiz all four ways.
Success check: give 15 − 6 and watch whether they reach for "6 + ? = 15" unprompted.