Looking for a fun way to teach one more than numbers to 20? This Under the Sea maths activity is a playful way to help children practise counting, number recognition, one more than, early addition and number confidence. With a simple ocean theme, children can explore numbers through movement, talk, play and hands-on learning, making it ideal for EYFS, Reception, Year 1, intervention groups and outdoor maths. New to Outdoor Lesarning? Explore the Beginners Guide to Outdoor Learning KS1
New to outdoor learning? Start here
If taking maths outdoors feels like a lot to organise, start with one simple number focus. You do not need a big outdoor space, expensive equipment or complicated planning. A playground, tuff tray, chalk area, garden space or small outdoor corner can become an under the sea number world.
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One more than is a brilliant concept to teach through active learning because children need to see how numbers grow. When children count shells, fish, sea creatures, bubbles or treasure, they can physically add one more and notice what happens to the total.
Start small. Choose numbers to 10 first if children need confidence, then build towards one more than numbers to 20. Keep the activity playful, practical and full of talk.
Try this tomorrow
If you only do one thing, try an under the sea number hunt. Place number cards from 1 to 20 around your outdoor space and ask children to find a number, say it aloud, then work out one more. They can show the answer using shells, stones, chalk bubbles or pretend sea creatures.
Time: 10 to 15 minutes, prep: low, learning: counting, number recognition, one more than, early addition and maths talk.
This works well because children are moving, finding, counting and explaining. It helps one more than feel concrete rather than just something they have to remember.
One More Than to 20 EYFS
Teaching one more than to 20 helps children build an early understanding of number order and addition. Children need lots of practical opportunities to see that when one item is added, the number increases by one.
An Under the Sea theme makes this learning more engaging. Children can count fish, add one more shell, give a crab one more pebble, place one more bubble in the sea, or help a mermaid collect one more treasure. These small playful contexts help children repeat the same skill without it feeling boring.
This activity can be adapted for different levels. Some children may work with numbers to 5 or 10, while others may confidently work with numbers to 20 and begin to explain how they know the answer.
Under the Sea Maths Activities
Under the Sea maths is a lovely way to bring imagination into number learning. Children can explore counting, matching, ordering, comparing, one more than, one less than, number formation and simple addition through ocean-themed play.
You might create a sea creature number trail, a bubble counting challenge, a treasure counting station, a fishy number line or a shell matching activity. The key is to keep the focus clear so children are not overwhelmed by too many resources or instructions.
Outdoor learning works especially well for under the sea maths because children can move like sea creatures, jump along number lines, collect natural treasures and use chalk to create waves, bubbles and number paths.
One More Than Outdoor Maths
Outdoor maths gives children space to move, count and physically show their thinking. For one more than, this is really useful because children can add one more object, take one more step, jump to the next number or move along a number line.
Children often understand maths more deeply when they can use their bodies and real objects. A child who finds written number work tricky may be able to show one more confidently by adding one more shell, stepping to the next chalk number or placing one more fish in a hoop.
This makes outdoor one more than activities especially helpful for children who need practical, visual or sensory approaches to maths.
Number Recognition to 20
Before children can confidently find one more than a number, they need repeated practice recognising numbers to 20. An Under the Sea theme gives lots of opportunities for this. Children can match sea creatures to numbers, order number shells, find hidden numerals, or follow a number trail across the outdoor space.
Number recognition becomes stronger when children see numbers in different places and contexts. They begin to understand that the number 14 on a card, in chalk, on a shell or on a treasure chest still means the same amount.
This kind of playful repetition is perfect for EYFS and Year 1 because children practise without feeling like they are doing the same worksheet again and again.
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One More Than for Year 1
One more than is also important in Year 1 because it supports addition, number lines, place value and mental maths. Children need to be able to say the number after, count on and understand how numbers increase.
An Under the Sea activity can give Year 1 children a quick, active warm-up before moving into written work. They might choose a number, find one more, explain their reasoning and then record the number sentence.
For children who need extra support, practical outdoor activities can help close gaps and build confidence. For children who are ready for challenge, you can extend into one less than, two more than, number patterns or simple problem-solving.
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The Muddy Puddle Teacher Club helps busy teachers, nursery practitioners and childminders save planning time with ready-to-use outdoor learning resources, EYFS maths ideas, KS1 number activities, intervention support, SEND-friendly resources and seasonal planning.
If you want more One More Than 20 – Under the Sea ideas, you can start your 60-day free trial today and access simple, practical and playful outdoor maths resources straight away.
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Try more outdoor maths ks1 ideas – estimating numbers to 100.
Estimating with numbers up to 100 : Earthly Estimating
FAQs
What does one more than mean?
One more than means adding one to a number. For example, one more than 6 is 7 because you count on one step to the next number.
How do you teach one more than to 20?
You can teach one more than to 20 by using practical objects, number lines, counting games, movement activities and simple questions. Children need to see, touch and move objects so they understand that the number increases by one.
What are good Under the Sea maths activities?
Good Under the Sea maths activities include counting shells, matching fish to numbers, creating bubble number lines, finding one more treasure, ordering sea creature numbers and using chalk waves for outdoor number trails.
Is one more than suitable for EYFS?
Yes, one more than is suitable for EYFS when taught through practical play. Children can start with numbers to 5 or 10, then build towards numbers to 20 when they are ready.
How can I teach one more than outdoors?
You can teach one more than outdoors by using chalk number lines, natural objects, hoops, number cards, movement games and counting trails. Children can physically add one more object or move to the next number.
How does one more than support early addition?
One more than helps children understand that numbers increase when something is added. This is an important early step towards addition, counting on and using number lines.
Can this activity support SEND pupils?
Yes, one more than activities can support SEND pupils when they are practical, visual and active. Children can use real objects, movement, repetition and simple language to build confidence.
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