OuiSi · Math

Two cards, one sum

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Grades K–2 Teaching 25 min Plus 3 to set out, 3 to clear Class any size Set any Prep counters, plus or minus signs on card

set out 3′ Two cards, two numbers 7′ Put the sign between 9′ Turn the sign over 5′ Close 4′ clear 3′

Goal: Children count two pictures, put a sign between them, and build a sum they can see. The two cards stay on the table the whole time, so the numbers never float free.
Materials: One OuiSi Photo-Card set, about six cards per pair. Counters. One large plus sign and one minus sign per pair, on card or paper.

K: Addition only, numbers under six, counters on both cards throughout — about 20 min
Grade 1: Numbers under ten, and swap the sign to take away — the full 25 min
Grade 2: Write the sum down, and find a different pair that gives the same answer — the full 25 min

1 · Two cards, two numbers

7 min

Pairs, about six cards face up.

Find two cards where you can count something on each one.

Put a counter on every one, on both cards.

Counters stay on the cards for the whole lesson at this age. The moment they come off, the numbers become abstract and half the room loses the thread.

2 · Put the sign between

9 min

Lay your own two cards out with the plus sign physically between them, where everyone can see.

Two cards and a sign make a sum. This one says five and three.

Now build yours. Put your plus sign between your cards and work out the answer.

The counters do the work.

Slide all the counters from both cards into one pile. Count them. That is your answer.

The answer is physically assembled rather than calculated, which is exactly right for this age. The arithmetic comes later and comes from this.

3 · Turn the sign over

5 min

Grade 1 and up. Swap the plus for a minus.

Now it says take away. Which card goes first?

Children will put the smaller number first out of habit and find it does not work. That failure is the lesson, so let it happen before you say anything.

Take the counters off the second card away from the first card's pile. How many are left?

4 · Close

4 min

Hold up your two cards and tell me your sum.

Four or five pairs, quickly, with the cards held up so the room sees the quantities as they hear the numbers.

Watch for

Numbers running away. Under six for K, under ten for grade 1. A card with thirty stones turns this into counting practice and nothing else.
Counters coming off too early. They stay on the cards until the sliding step. Replace them if a pair clears the cards.
Nothing countable. Many cards have no discrete objects. Swap it rather than letting a pair stall.
Subtraction order. Expect the mistake, and let step three produce it rather than preventing it.

Adapt

K — addition only. Skip step three entirely and spend the time on more pairs.
Dyscalculia — stay under six, and keep every counter visible on the card until the very last move.
Number anxiety — no timing, no sharing out loud. Building the sum is the whole task.
Motor needs — larger counters and larger signs, with a partner placing on request.
Multilingual learners — numerals and signs are universal. Say the sum in any language.
Finished early — find two different cards that give the same answer.

Curriculum links. Counting two small quantities with one-to-one correspondence · Composing an addition sentence from two sets · Combining sets physically to find a sum · Separating sets to take away · Discovering that order matters in subtraction.
Standard codes vary by state and district — these are the skills exercised, for you to map to your own.

For grades 3–5 see Two cards, one equation, which adds multiplication, division, and the order of operations.
Screen-free. No codes and no devices. Works with any OuiSi Photo-Card set.