Sink and Float
Sink and float is a first science sorting work. A child of about 3 who carries and pours water takes ordinary objects from a basket, guesses whether each will sink or float, drops it gently into a tub of water, and sorts it onto a mat. There's nothing to buy: a tub, a towel and a dozen household objects.
Sourced from the texts, not yet presented at home
| Typical age | 3 to 5.5 years |
|---|---|
| Area | Cultural |
| Before this | |
| Materials | No special materials |
| Direct aim | To find out by testing which objects sink and which float, and to sort them. |
| Control of error | The water. Whatever the guess, the object shows what it does, and the child sees it. Nobody needs to say who was right. |
| Leads to | Later lessons in this line are in preparation. |
| Time | About 15 minutes (our estimate). |
| Grouping | One child, or two taking turns |
| Parent prep | Moderate. Fill a tub, lay a towel, choose the objects. |
| Other names | Sink or float, Floating and sinking, Float and sink sorting |
What the work teaches
Direct aim. To find out by testing which objects sink and which float, and to sort them.
Indirect aims, the ones you will not see at once
- Guessing first, then testing: the start of scientific thinking
- Careful handling of water, with a towel and a sponge for spills
- Words for materials: wood, metal, plastic, stone
- Sorting into two groups by a quality that has to be discovered
Set it out before you invite the child
A clear tub or a wide glass bowl, half full of water, on a towel.
A basket of 8 to 12 objects from around the house, about half that sink and half that float: a cork, a wooden block, a plastic lid, an apple, a metal spoon, a stone, a key, a marble-sized ball of clay. Nothing small enough to swallow if a toddler is near.
Two small mats or cards, one labelled with a picture of an object floating and one sinking.
A small towel or cloth for drying, and a sponge.
The sorting tray is later than Montessori's books. Her 1912 book does describe children crowding round a basin of water with floating toys in it.
Presentation, step by step
- 1Carry the basket to the table and lay out the two mats beside the tub.
- 2Pick up the cork. Hold it and say: "I think it will float."
- 3Lower it gently onto the water and watch. "It floats." Lift it out, dry it, and set it on the float mat.
- 4Pick up the stone, say what you think, and lower it in. "It sinks." Lift it out, dry it, and set it on the sink mat.
- 5Offer the basket: "Which one shall we try next? What do you think it will do?"
- 6Let the child test the rest, guessing first each time.
- 7Empty the tub together, sponge any spills, and put everything back.
Details that hold the child's attention
A heavy apple that floats and a tiny key that sinks.
Watching something sink slowly to the bottom.
A guess that turns out wrong.
A ball of clay that sinks, then floats when shaped into a boat.
How the child sees a mistake
The water. Whatever the guess, the object shows what it does, and the child sees it. Nobody needs to say who was right.
The words come after the hands
| Words | Shown with |
|---|---|
| sink, float | The two outcomes. |
| guess, test | What we do before and during. |
| wood, metal, plastic, stone | What the objects are made of. |
| heavy, light | Useful words, though size and weight alone don't decide it. |
The three-period lesson, scripted
You need a floating cork and a sunken stone in the tub.
| Period | What you do and say |
|---|---|
| 1. Naming | "The cork floats." "The stone sinks." |
| 2. Recognition | "Show me what floats." "Show me what sank." |
| 3. Recall | Point to an object in the water and ask "What is it doing?" |
Our suggestion. The words come easily; the guessing is the real work.
Extensions and variations
- Recording guesses and results with drawings on a two-column sheet
- Making a sinking ball of clay into a boat that floats
- Testing objects found on a walk: leaves, sticks, stones, acorns
- Floating a boat and loading it with pennies until it sinks, with an adult
- Peeled and unpeeled oranges: the unpeeled one floats
Variations
- A bath-time version with bath toys and kitchen objects
- Outdoors in a bucket or a water table
Make it or buy it
| Material | Make it | Buy, approx. |
|---|
Prices noted . Approximate US street prices for home-use versions; they vary by maker and change often, so recheck before buying.
Making it at home
A clear tub, a towel, two mats and a basket of objects from around the house. Nothing to buy.
What to check when buying a set
Nothing to buy. Sink and float kits exist but weren't on sale at the stores we checked.
Printables for this age
This work needs only the material, so it has no printable of its own. The shelf plan below places it among the other works for the same age.
- Shelf plan for age 3PDF, 1 page, 250 KBEvery work for this age on one page, in order, with a column to date each presentation.
Every printable for one age, by email
The shelf plan and the lesson printables for your child's age in one email, then three short emails on the first lesson, what to make or buy, and what comes next.
Signs the child is ready, and signs it is done
Ready for the first presentation
- Pours water from a pitcher without spilling much.
- Carries a tub or bowl with two hands.
- Sorts objects into two groups.
- Is curious about why things happen.
Ready for the next lesson
- Guesses before every test without being asked.
- Sorts all the objects onto the right mats.
- Brings new objects to test.
- Starts to say why: "It's wood, so it floats."
Fitting it into a home, not a classroom
| If you have | Do this |
|---|---|
| No table space for water | Do it at the kitchen sink, in the bath, or outdoors with a bucket. |
| A toddler sibling | Give the toddler large objects only, and never leave water out unattended. |
| Several children | Each child guesses for every object before one of them tests it. |
| A child who wants to know why | Say what you know simply: some materials float, like most wood; metal usually sinks unless it's shaped like a boat. Then test more. |
When it does not go to plan
| When | Try this |
|---|---|
| Objects get thrown into the water. | Show lowering gently again. Splashing ends the work for the day. |
| Everything gets tested without guessing. | Hold the object for a moment and ask what it will do. The guess is the point. |
| Water ends up everywhere. | Less water in the tub, a towel underneath, and a sponge on the tray. |
| The child is upset by a wrong guess. | Make your own wrong guesses out loud and laugh at them. Surprises are the fun of it. |
Hazards to check before each session
Never leave a child alone with a tub of water, and empty it straight after. Small children can drown in a few centimeters of water.
Use objects too big to swallow if a younger child is near, and wipe up spills so nobody slips.
Where other sequences and standards place it
We have not bought the paid homeschool curricula, so they are not listed here.
| Framework | Where it sits |
|---|---|
| This site's Cultural sequence | Lesson 6 of 12 published, after Wet Pouring Between Two Pitchers. Checked in: the scope and sequence |
| Montessori, The Montessori Method (1912) | Children gathered round a basin of water with floating toys; a boy of two and a half finds his own way to see, and should be allowed to. Checked in: Chapter V, Discipline |
| Next Generation Science Standards, grade 2 | 2-PS1-1: plan and conduct an investigation to describe and classify different kinds of materials by their observable properties. Checked in: www.nextgenscience.org |
| Head Start Early Learning Outcomes Framework, preschool | P-SCI 4: the child asks a question, gathers information and makes predictions. P-SCI 5: the child plans and conducts investigations and experiments. Checked in: www.in.gov |
Sink and float: questions parents ask
What is sink and float in Montessori?
A sorting work with a tub of water and a basket of household objects. The child guesses whether each will sink or float, tests it, and sorts it onto one of two mats.
What objects should I use for sink and float?
About a dozen ordinary things, half that sink and half that float: a cork, a wooden block, a plastic lid, an apple, a metal spoon, a stone, a key. Nothing small enough to swallow if a toddler is near.
What age is sink and float for?
From about 3, once the child pours and carries water carefully, and on this site it runs to 5.5.
Should I explain why things float?
Not at first. Let the child guess and test. When the child asks why, keep it simple. What it's made of matters, and so does its shape.
Sources cited by book and chapter
- Maria Montessori, The Montessori Method (1912)
Chapter V, Discipline
One day the children gathered, laughing and talking, in a circle about a basin of water containing some floating toys.
A boy of two and a half, left outside the circle round the basin, decided to fetch a little chair and climb on it so that he could see.
By lifting the boy up to show him the floating toys, the teacher took from him the joy of conquering the obstacle by his own effort.
- Maria Montessori, The Montessori Elementary Material (1917)
Part VII, Object Lessons
For object lessons there should be a shelf of specimens: bottles of different drinks, kinds of cloth, the raw materials they are made of, and various minerals.
- Maria Montessori, Dr. Montessori's Own Handbook (1914)
Writing
The material leads the child to distinguish identities from differences and to classify his sensations.
Reviewed by
What to offer next
Once the child chooses this work unprompted and finishes it without help, the next lesson to prepare is Living and Nonliving: A First Sort.
- Land forms3 to 5.5 years
- Continent globe3 to 5 years
- Sink and float3 to 5.5 years
- Living and nonliving3.5 to 6 years
- Botany cabinet3.5 to 6 years