This task enables learners to explore ideas associated with equivalence, in an intuitive context that may also be familiar. It provides opportunities to develop young children's language of comparison, for example 'heavier', 'lighter', 'greater', 'smaller', 'same', 'equally heavy', 'equal'...
You may like to read the book 'Balancing Act' by Ellen Stoll Walsh as a precursor to this task.
This problem featured in an NRICH Primary webinar in January 2021.
Begin by setting the scene and telling children about the animals in the wood. You could simply show the image of the seesaw and invite pupils to talk to each other about what they notice and what they wonder. Give opportunities for them to share their observations and questions, trying to value all contributions. At this point, some children may talk about their own experiences of seesaws, and you can refer to this as you pose some challenges.
You could say that you're going to sit an owl on one side of the seesaw (indicate which side by pointing). What do they think is going to happen? Invite suggestions and then demonstrate. Give learners time to talk to a partner about what happened, and offer the chance for some pairs to share their thoughts.
Next, explain that you are going to sit a hedgehog on the other side of the seesaw. Can they talk to their partner about what they think will happen? Once again, demonstrate using the interactivity, and allow learners time to talk with their partner again. As you invite pairs to share their interpretations of what happened, encourage them to try to explain what they saw. Draw attention to any appropriate vocabulary they use and introduce useful language yourself if it is not forthcoming from the children themselves.
Use some further examples with the whole class so that children get a good feel for the context. You may like to encourage them to suggest their own set-ups, but ask everyone to predict what will happen each time before demonstrating.
Next, give pairs of children time to explore the seesaw for themselves. The interactivity could be used on a large child-height whiteboard and/or on laptops/tablets/computers. If you have real balances available in your setting, you can use them to explore the ideas in this task using small world toys, soft toys, cubes or... As children discover relationships, encourage them to record what they have found out. Try not to be too prescriptive about how they do this - they may draw pictures, use words, invent symbols... However they choose to record, try to make time to talk with each pair about their discoveries too.
In the plenary, you could ask some pairs to talk about a particular relationship they have discovered. Alternatively, or in addition, you could spend some time looking at different ways to balance the seesaw. Create a balanced seesaw using the interactivity and ask learners what they think will happen if an owl sits on the left and another owl sits on the right? Why? What will happen if both owls get off the seesaw? Understanding that if the two sides are balanced, and then the same change is made to both sides the seesaw stays balanced, is key.
What do you think is going to happen when...?
Can you describe what happened? Why did that happen?
Practical experience (through the interactivity or a real balance/seesaw) will help all children access this task.
You may like to introduce mathematical notation in terms of the equals and inequality signs. The Settings menu of the interactivity allows you to 'turn on' symbols so that these become visible at the pivot point of the seesaw.