Finds one more or one less from a group of up to five objects, then ten objects.
Observe whether the child: finds one more or one less from a group of up to five objects, then ten objects.
What it looks like
Three ways this behaviour shows up as a child grows. Each level includes everyday moments to watch for.
Emerging
Just starting
The child sometimes responds correctly for very small sets with heavy support, but is inconsistent. They often need to recount from one, and may confuse "more" and "less" or change the set by more than one.
What you might see
When asked for one more from 4 counters, adds a handful or rearranges the set without adding exactly one.
When asked for one less from 5 objects, removes two or says a different number word without changing the set.
Gets one more correct from 2 or 3 objects with adult modelling, but for 4 or 5 objects removes/ adds the wrong amount.
Recounts from 1 each time and forgets the starting total, leading to inconsistent answers across repeated trials.
Expected
On track
The child can find one more or one less from sets up to five, usually by counting or physically adding/removing one object. For larger sets up to ten, they can succeed with prompts to keep track (e.g., move counted items aside).
What you might see
From a set of 5, adds one and says "Now it’s 6" after counting the full set.
From a set of 9, removes one with a prompt and recounts carefully to confirm the new total is 8.
Exceeding
Going further
The child reliably finds one more or one less from sets up to ten, using efficient strategies (e.g., knowing the next/previous number word) and checking when unsure. They understand the change is exactly one and can explain what changed.
What you might see
Given 7 objects, says "One more is 8" and then adds one object to make 8, checking by counting once.
Given 10 objects, removes one and states "That’s one less, so 9," and can explain "I took one away."
During a dice game, predicts "If I have 6 and I get one more, I’ll have 7" and verifies by counting pieces.
Corrects a peer: "That’s two less, not one less" and demonstrates removing exactly one item to show one less.
Try this at home
Small everyday moments where you can notice this behaviour without setting up anything special.
Snack time: place 1–10 pieces of fruit and ask, "Can you make it one more? How many now?" Then, "Can you make it one less?"
Play with small toys: start with 3–5 cars and ask your child to make "one more" without giving them extra cars in hand; notice whether they request exactly one and check the total.
Transitions: when putting shoes by the door, ask, "We have 4 shoes here—what would one more shoe be?" (Then count shoes together to check.)
Story time: use fingers as objects and ask, "I’m holding up 5 fingers—show me one more" and see if your child changes by exactly one.
Outdoor play: collect 6 stones, ask the child to take away one to make one less, then to add one back to make one more.
Connected behaviours
Behaviours that scaffold, follow, or co-emerge with this one.
The framework source and supporting developmental research.
Framework source
Development Matters in the EYFS (2012), Mathematics: Numbers.
The construct is explicitly listed as an observable behaviour supporting number understanding in 40–60+ months.
Developmental research
Gelman, R., & Gallistel, C. R. (1978). The Child’s Understanding of Number. Harvard University Press.
One-more/one-less reasoning builds on understanding that counting progresses by one with stable order and that totals correspond to number words.
Five-level rubric (detailed)ShowHide
The full progression underlying the three levels above. Used by the platform’s reasoning agent when planning activities and observations.
Not Yet
The child does not yet understand or act on "one more"/"one less" as a change of exactly one. They may add or take away an arbitrary number, or restart counting the whole set each time without connecting the change to the previous total.
When asked for one more from 4 counters, adds a handful or rearranges the set without adding exactly one.
When asked for one less from 5 objects, removes two or says a different number word without changing the set.
Emerging
The child sometimes responds correctly for very small sets with heavy support, but is inconsistent. They often need to recount from one, and may confuse "more" and "less" or change the set by more than one.
Gets one more correct from 2 or 3 objects with adult modelling, but for 4 or 5 objects removes/ adds the wrong amount.
Recounts from 1 each time and forgets the starting total, leading to inconsistent answers across repeated trials.
Developing
The child can find one more or one less from sets up to five, usually by counting or physically adding/removing one object. For larger sets up to ten, they can succeed with prompts to keep track (e.g., move counted items aside).
From a set of 5, adds one and says "Now it’s 6" after counting the full set.
From a set of 9, removes one with a prompt and recounts carefully to confirm the new total is 8.
Secure
The child reliably finds one more or one less from sets up to ten, using efficient strategies (e.g., knowing the next/previous number word) and checking when unsure. They understand the change is exactly one and can explain what changed.
Given 7 objects, says "One more is 8" and then adds one object to make 8, checking by counting once.
Given 10 objects, removes one and states "That’s one less, so 9," and can explain "I took one away."
Reflexive
The child applies one-more/one-less flexibly in games and everyday situations, sometimes predicting the result before changing the set. They can generalise across representations (objects, actions, number line language) and support peers to reason about it.
During a dice game, predicts "If I have 6 and I get one more, I’ll have 7" and verifies by counting pieces.
Corrects a peer: "That’s two less, not one less" and demonstrates removing exactly one item to show one less.
