Sink or Float

Teaching the concept of whether objects will sink or float is one of my favorite science lessons in kindergarten. It’s not only fun and hands-on, but it also taps into students’ natural curiosity about the world around them. There’s something magical about letting little hands explore a tub full of water—it has the same thrilling, rule-breaking energy as jumping into puddles or making mud pies. It feels like something you shouldn’t be doing in school, which is exactly why students love it.

Building Background Knowledge

Before diving into our experiment, we begin with a class discussion to build background knowledge. We talk about what it means for something to sink and what it means to float. I encourage students to share their own experiences and observations, which often leads to excited examples like boats, rubber ducks, and rocks.

This discussion is a great opportunity to introduce scientific vocabulary in a meaningful way. I like to chart our ideas on a large anchor chart with two columns labeled “Sink” and “Float.” As we brainstorm, students suggest objects they’ve encountered in everyday life and we add them to the appropriate column. This collaborative activity helps activate prior knowledge and sets the stage for deeper learning.

Read-Aloud Connection: A Book on Floating and Sinking

Whenever I introduce a new science concept, I love to pair it with quality children’s literature. While searching for a good sink or float book on Amazon, I stumbled upon a title that ended up being a fantastic addition to our classroom library: Floating and Sinking.

This book breaks down the concept of buoyancy in a way that’s perfect for young learners. With clear explanations, real-life examples, and vibrant photos, it helps reinforce the ideas we’re discussing. My students were so engaged that they asked me to read it multiple times—and I’ll admit, I even learned a few new facts myself!

Books like this are a great way to scaffold understanding before introducing hands-on activities. If you’re looking for more great science literature, I’ve put together a list of The Best Science Books for Kindergarten that you can find on my website.

Hands-On Science: The Sink or Float Experiment

After our discussion and read-aloud, it’s time to test our theories with a hands-on sink or float experiment. This is where the real excitement begins!

I gather a variety of small items from around the classroom—things like crayons, blocks, erasers, paperclips, and plastic toys. This experiment is low-prep, which is always a bonus on busy teaching days. I fill a large plastic tub with water, but I keep it hidden until it’s time to begin. Any teacher of young children knows that the sight of a water bin can immediately lead to wandering hands!

Once we’re ready, I reveal the container and let students predict whether each item will sink or float. We take turns testing the objects and observe what happens. It’s a perfect opportunity to introduce the scientific method in a simple, age-appropriate way: we make a hypothesis, conduct a test, and record our results.

Recording and Assessment

To track our findings, I use sink or float sorting cards on a pocket chart as a visual summary of our experiment. This not only keeps our data organized but also helps visual learners make sense of the concept.

At the end of the lesson, students complete an assessment in their interactive science notebooks. They draw pictures of objects that sank and floated, write simple sentences, and reflect on what they learned. This activity also serves as documentation for student progress in science—a great resource for parent-teacher conferences or administrator check-ins.

If you’re looking for more assessments like this, take a look at my Kindergarten Interactive Science Notebook, which includes printable activities and assessments on a wide range of science topics.

A version for first grade is also available!

Free Sink or Float Resource

Want to try this sink or float lesson in your classroom? I’ve created a free downloadable resource that includes printable materials for your experiment and assessment. Just fill out the form below to grab your copy.

More Kindergarten Science Ideas

If you enjoyed this lesson, be sure to explore these other science topics on my website:

• The Best Science Books for Kindergarten
• Force and Motion in Kindergarten
• Teaching States of Matter in Kindergarten