The Path Light Takes
A 55-minute Grade 4 lesson on modelling how light reflecting off objects and entering the eye allows them to be seen.
The Path Light Takes is a free 55-minute Grade 4 science lesson plan for Common Core standard 4-PS4-2 — model how light bouncing off a thing and into your eye lets you see it. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.
- Grade:
- Grade 4
- Length:
- 55 minutes
- Standard:
- 4-PS4-2
Grade 4 · Physical Science
4-PS4-2
Develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen.
Objective
Students will be able to trace the whole path of light from source to object to eye.
Students are successful when they can
- Starts the path at a light source.
- Shows light reflecting off the object.
- Ends the path at the eye.
What you need
- Torches, mirrors, card, a cardboard tube for a periscope
- Arrow cards for building light paths
- The printable practice sheet linked at the end of this plan
The lesson
Warm-up
5 min- Ask the class to draw how they see a book on the desk.
- Collect the drawings and look for how many start at the eye.
Teach — three arrows, in one direction
14 min- Draw arrow one: light leaves the lamp.
- Draw arrow two: light strikes the book and reflects.
- Draw arrow three: reflected light enters the eye.
- Ask what happens if arrow one is removed. Nothing is seen.
- Build a periscope and trace the same path round two corners.
- Correct the common drawing: no arrow leaves the eye.
“Where does the light start, and which way is the arrow pointing?”
Investigate — build a periscope
19 min- Pairs build a periscope from a tube and two angled mirrors.
- They trace the light path on paper with arrows.
- They remove one mirror and record what happens.
- They explain the result using the path they drew.
Independent practice
14 min- Students complete the 'The Path Light Takes' page.
- Check the sequence ends at the eye.
Close
3 min- Ask how you see the moon, using the same three arrows.
What goes wrong, and why
Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.
Draws arrows leaving the eye.
Why: Looking feels active.
Fix: Cover the lamp. Looking harder changes nothing.
Starts the path at the object.
Why: The object is what you see.
Fix: The object does not make light. Where did the light come from?
Thinks a mirror creates light.
Why: The card lights up when the mirror is added.
Fix: Remove the torch and keep the mirror. Nothing.
If they are not there yet
- A three-arrow frame to complete.
- A prepared periscope to trace.
If they finish early
- Add a third mirror and trace the new path.
- Explain why a dark room stays dark with a mirror in it.
- Say why you can see a red apple as red.
Exit ticket
Draw or describe the path of light that lets you see a book by lamplight.
What to look for: Lamp to book, reflected off the book, into the eye. An arrow from the eye means the direction needs another run.
Printable practice for 4-PS4-2
Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.
- The Path Light TakesNumber the steps from 1 to 4.
Questions about The Path Light Takes
How long does the The Path Light Takes lesson take?
55 minutes, split across 5 timed sections: warm-up 5 min, teach 14 min, investigate 19 min, independent practice 14 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.
Which standard does The Path Light Takes teach?
4-PS4-2 — 4-PS4-2, Physical Science for Grade 4: “Develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen.” In plain terms, model how light bouncing off a thing and into your eye lets you see it.
What do I need to teach this lesson?
Torches, mirrors, card, a cardboard tube for a periscope, arrow cards for building light paths and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.
What mistakes should I expect in this lesson?
Three, each a reasoning error rather than carelessness: draws arrows leaving the eye; starts the path at the object and thinks a mirror creates light. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.
How do I know whether the lesson worked?
The exit ticket asks: “Draw or describe the path of light that lets you see a book by lamplight.” Lamp to book, reflected off the book, into the eye. An arrow from the eye means the direction needs another run. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.
Is there a worksheet to go with The Path Light Takes?
Yes — 1 printable 4-PS4-2 worksheet, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.
Is The Path Light Takes free to use?
Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 8 September 2026. Please do not resell it or republish it as your own.
Last reviewed 2026-09-08. Aligned to 4-PS4-2 of the Next Generation Science Standards.