Goals for the session

Children aged 7 to 12 should learn that rocks differ in hardness, grain and how they react to water, and that these differences give clues about how the rock formed. They should use descriptive words accurately and back up a sorting decision with evidence.

Children take away a completed test grid, a settled layers bottle for the classroom shelf and a set of words such as grain, layer and scratch that they can use on any walk. Encourage them to bring in one rock from home for the next session and describe it using the same tests.

Sample session: rock detectives (60 minutes)

For 12 children in pairs. You need a collection of 8 to 10 different rocks, ideally including chalk, sandstone, granite, slate, marble and pumice, which can be gathered locally or bought as a small school set. Per pair: hand lens, a steel paperclip, a copper coin, a cup of water, a pipette, paper towels and a recording grid. For the modelling task: a clear plastic bottle, sand, soil and small gravel.

• 0-10 min: Pass rocks round. Each pair chooses three words to describe one rock without naming it; others guess which rock it is.

• 10-30 min: Tests. Scratch with a fingernail, then a coin, then a paperclip. Drip water on each and watch whether it soaks in. Record results in the grid.

• 30-40 min: Sort the rocks into groups using the test results. Pairs explain their groups to another pair.

• 40-55 min: Layers model. Pour sand, soil and gravel into the bottle, top up with water, shake and leave it to settle. Watch the layers form.

• 55-60 min: Link the settled layers back to sandstone and other layered rocks in the collection.

Safety notes

Supervise the scratch tests and keep paperclips pointed away from hands. No hammering or breaking rocks in this session, as flying chips can injure eyes. Screw bottle lids on tightly before shaking. Wash hands afterwards if children have handled soil.

Adapting for different ages

Younger children can sort by one property at a time, such as rough or smooth, and skip the grid. Older children can place the rocks on a simple hardness scale and research whether each is igneous, sedimentary or metamorphic, then check whether their test results match. A follow-up walk to look at building stone, walls or gravestones in the local area extends the session well.

Key points

• Real rocks and simple tests give children evidence, not just names.

• Ask children to justify each group they make.

• A layers model links a classroom test to how rocks form.

• Keep hammers out of introductory sessions.

Ready-made resources

Printable session plans and materials for this topic are available from EduTrend Contents: W4C-120 Young Scientists Lab.

Photos: Takemaru Hirai, Reem Alja'ad / Unsplash