Unit Overview
6.1 Light & Matter

Why do we sometimes see different things when looking at the same object?

Unit Summary

How does a one-way mirror work? Though most everyone knows that one-way mirrors exist, having students model how they work turns out to be a very effective way to develop their thinking about how visible light travels and how we see images. Initial student models in this 6th grade light and matter science unit reveal a wide variety of ideas and explanations that motivate the unit investigations that help students figure out what is going on and lead them to a deeper understanding of the world around them.

A video of an experience with a one-way mirror, gets students to organize and write down their initial ideas and then they dig in to test those ideas and figure out what is really happening. Students build a scaled box model of what they saw in the video to test out their ideas. Using two boxes combined together with a one-way mirror in between the two, students vary the presence of light in the two boxes to figure out how a one-way mirror works and improve their initial models so they accurately explain how light is reflected and transmitted through materials and the basics of how these behaviors of light result in the images we see.

As the first 6th grade science unit in the OpenSciEd program, during the course of this unit, students also develop the foundation for classroom norms for collaboration that will be important across the whole program while answering several questions.

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Unit Examples

Additional Unit Information

Building Toward the Following Standards and Practices
Performance Expectations

This unit builds toward the following NGSS Performance Expectations (PEs): 


  • Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.


  • Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.

*Performance Expectations marked with an asterisk are partially developed in this unit and shared with other units. Review the Where does this unit fall within the OpenSciEd Scope and Sequence? for more information.

Disciplinary Core Ideas

The unit expands students’ understanding of particle models and energy transfer, which include these Grade 6–8 DCI elements: 

PS4.B. When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light.  Students investigate using the box model, readings, videos, and data collected with light sensors to develop a robust model and explanation for how light interacts with an object’s material. This unit does not address absorption of light, which is taken up in the Cup Design Unit. Should you teach Cup Design Unit next, Lesson 8 in this unit offers a bridge in the form of a related phenomenon. The phenomena in this unit can be explained using a ray model for light, thus a wave model and different frequencies of light are not developed until 8th grade in the OpenSciEd Scope and Sequence. This is a notable omission given the overarching Performance Expectation for the unit. Until students develop a deep understanding of waves, including frequency and amplitude, they are at a disadvantage for developing a wave model for light. Students will engage deeply with wave models in the Sound Unit unit. Thus, expanding the wave model from sound to light in the Space Unit makes sense. The Space Unit is also an ideal placement for these DCI elements as students to develop a wave model of light which has more explanatory power in the study of space-related phenomena.

PS4.B. The path that light travels can be traced as straight lines, except at surfaces between different transparent materials (e.g., air and water, air and glass) where the light path bends. This unit engages students using the idea that light travels in straight lines to model the one-way mirror phenomenon. There are Building Prerequisite Understandings offered in Lesson 2 to support students further with this concept. Students develop an understanding of refraction of light in Lesson 6 as they notice the bending of light through the lens of the eye to focus light on the retina. Students model how light bends at the surface of the lenses. Extension Opportunities are provided to enhance your students’ experiences with refraction at surfaces between air, water, and glass.

LS1.D. Each sense receptor responds to different inputs (electromagnetic, mechanical, chemical), transmitting them as signals that travel along nerve cells to the brain. The signals are then processed in the brain, resulting in immediate behaviors or memories.  In lesson 6 students develop an understanding of how eyes sense light inputs and transmit them as signals to the brain. Due to the different amounts of light entering the eye, some signals register as stronger or weaker ones. The unit does not address nerve cells because cells will be investigated later in the 6th grade sequence. Instead, students learn about the “optic nerve” connecting eyes to the brain. Students will not figure out how the brain responds in terms of reflex or memories.

*There is a strike-through part of the DCI elements that are not developed in this unit.

Science & Engineering Practices

Asking Questions and Defining Problems: This unit intentionally develops this practice. Students ask “what happens if” questions to guide initial investigations with the box models in Lesson 2. They co-construct an experimental, testable question to guide a controlled investigation in Lesson 3. They ask “how” and “why” questions to motivate investigations and to explain the phenomenon (Lessons 4-7). Three Asking Questions Tools are provided to scaffold asking different kinds of questions.

  • Open and Closed Questions (Asking Questions Tool): Use this tool to support students in revising close-ended questions into open-ended ones. Avoid using it when students first offer questions for the DQB. Rather, use it later in a unit to transform close-ended questions into open-ended ones to investigate together.
  • Testable Questions (Asking Questions Tool): Use this tool to support students in asking testable questions that include enough specific information that one could gather evidence (e.g., measurements, observations) to answer the question. Note that this tool includes testable questions that are not specifically experimental ones, but ones that can be answered by gathering empirical evidence.
  • Experimental Questions (Asking Questions Tool) Use this tool to support students in asking experimental questions in which they will need to manipulate a variable in the system to observe its relationship to other variables.

Developing and Using Models: This unit intentionally develops this practice. In the first lesson, students discuss how to use physical models to test ideas about a phenomenon (i.e., the box model) and how to use diagrammatic models to represent and explain the phenomenon. They contrast the real-world system they are trying to understand (i.e., two rooms in the video) with their box models to consider limitations of physical models. In subsequent lessons, students discuss representation choices for diagrammatic models, such as using symbols and colors, and what these representations communicate about the phenomenon. New elements of modeling that emerge in 6-8th grades that are developed in this unit include modeling parts of the system at unobservable scales, including unobservable mechanisms that explain observable phenomena (e.g., light reflecting off microscopic, half-silvered, one-way mirror film) in Lesson 4, and modifying a model to match if a variable is changed (e.g., changing the light conditions or swapping the one-way mirror for glass) (Lesson 8).

Constructing Explanations and Designing Solutions. This unit intentionally develops constructing written explanations. In Lesson 7 students develop a written explanation for the phenomenon. First, they collaboratively write an explanation to one of their questions, with the teacher modeling how to write an explanation supported by a how and why account and evidence. Then students independently write an explanation for a second question about the phenomena, receive feedback from the teacher and peers, and revise their explanations.

Crosscutting Concepts

System and System Models: This unit intentionally develops this crosscutting concept. In this unit, students analyze the phenomenon to consider the components, interactions, and processes of the system, and how changes to light and changes to the material affect what is seen. Students zoom into different parts of the whole system to investigate subsystems (e.g., the one-way mirror material; the eye and brain system). By the conclusion of the unit, students will have a better understanding of what constitutes a system and will have iteratively developed a systems model that describes how light interacts with objects and how reflected light is an input into the eye.

Structure and Function: This unit intentionally develops this crosscutting concept. Students consider how the shape and composition of key components in the system (e.g., one-way mirror material, eye lens) help determine the function of those components. Students investigate the microscale composition (structure) of the one-way mirror, and figure out that the one-way mirror is designed with half-silvering, which affects the amount of light transmitted and reflected. Students explore the shapes and components of the human eye to understand how light inputs are processed into what we see. Students learn that the lens of the eye, because of its structure (shape and composition), refracts light to a point on the retina, where light signals are changed into electrical signals that are sent to the brain along the optic nerve.

This crosscutting concept is also key to the sensemaking in this unit.  

  • Cause and Effect
Connections to the Nature of Science

Which elements of NOS are developed in the unit?

  • Science investigations use a variety of methods and tools to make measurements and observations. (NOS-SEP)
  • Science assumes that objects and events in natural systems occur in consistent patterns that are understandable through measurement and observation. (NOS-CCC)
  • Science limits its explanations to systems that lend themselves to observation and empirical evidence. (NOS-CCC)

How are they developed?

  • Scale models are a method used by scientists and engineers to test ideas and make adjustments. Students use scale models in this unit as a way to investigate their ideas about the one-way mirror.
  • Students make measurements to identify patterns of reflection and transmission of light with multiple materials. They conduct systematic tests to make observations about how changing components of the system change the effect of the one-way mirror.
  • Students develop scientific explanations in writing through a scaffolded writing process. They discuss what makes for a good scientific explanation, with an opportunity for the teacher to model one before they try themselves. They evaluate each others’ explanation for features of scientific explanations, including using  empirical evidence to support the explanation.
Unit Information
How is the unit structured?

This unit includes only 1 lesson set. Lessons 2-4 help students develop ideas about the amount of light on either side of the mirror, how much of that light transmits or reflects, and why the structure of the one-way mirror causes certain amounts of light to transmit or reflect. A brief modeling activity in Lesson 5 helps to problematize that there are still gaps in our understanding, which motivates Lesson 6 focused on how our eyes sense light and our brain processes it. This helps students develop a more complete model to explain the phenomenon, which they do when they construct a written explanation for it in Lesson 7. Lesson 8 allows students to revisit other related phenomena (e.g., glass acting as a one-way mirror, reflective surfaces) and modify their models to explain those phenomena, too.

Where does this unit fall within the OpenSciEd Scope and Sequence?

This unit is designed to be taught as the first unit in the OpenSciEd Scope and Sequence. As such, it is intentionally designed to bridge the elements of NGSS expected in Grades 3-5 with new elements expected in Grades 6-8. It is also designed to spend additional time in the anchor lesson developing shared classroom norms for equitable sense-making, and developing a shared understanding of many fundamental OpenSciEd features, such as developing and using a Driving Question Board as a record of our class mission to explain a phenomenon, develop and using models, and articulating what we mean by “models” and “systems” and how they relate to the real-world phenomena we want to explain.  

This unit is designed to be taught prior to OpenSciEd Unit 6.2: How can containers keep stuff from warming up or cooling down? (Cup Design Unit) and OpenSciEd Unit 6.3: Why does a lot of hail, rain, or snow fall at some times and not others? (Storms Unit), which will expand on students’ understanding of light absorption resulting in an energy transfer. It is also designed to use a ray model for light (straight lines and arrows), which will be expanded upon in OpenSciEd Unit 8.4: How are we connected to the patterns we see in the sky and space? (Space Unit) when students develop a wave model for light to explain space-related phenomena.  

What modifications will I need to make if this unit is taught out of sequence?

This is the first unit in the OpenSciEd materials and intended to be used at the start of 6th grade. Given this placement, several modifications would need to be made if teaching this unit later in the OpenSciEd curriculum. These modifications include the following:

  • The 6th grade light and matter science unit spends time introducing the students to a Driving Question Board. This would not be necessary if taught after other OpenSciEd units.
  • The unit helps the class develop and practice a shared set of classroom norms. If this unit is taught later in a school year, the norm-building process would need to happen in an earlier unit and could be streamlined here.
  • This unit focuses on reinforcing many grades 3-5 elements in all three dimensions. This reinforcement is intentional as preparation for students to begin building on those elements in the grades 6-8 space. If this unit is taught later in the OpenSciEd sequence, modification to these elements would need to happen so that this unit is less about reinforcing grades 3-5 and more about building elements in grades 6-8.
  • This unit is the first unit in an intentional sequence to build two Performance Expectations: MS-PS4-2 and MS-LS1-8. The DCIs associated with these Performance Expectations are fully covered across multiple units. The approach to these DCIs will need to change if this unit is taught after other units addressing the same, or closely related, DCIs.
What are prerequisite math concepts necessary for the unit?

In Lesson 3 students will collect light sensor data under very specific measurement conditions in which any deviation from the protocol could result in measurement error. Even given the detailed protocol students follow, the light sensor will not consistently report a single value, so students will need to determine a range that seems as accurate as possible given the measurement conditions. When they rank order the materials by transmissivity and reflectivity, they will use ranges that could overlap for some materials, and students may need to estimate the central tendency within the range of values to help them determine their rankings. This work is largely done as a whole group and can be more or less guided by you. However, the following math concept may be helpful:

  • CCSS.Math.Content.6.SP.A.2: Understand that a set of data collected to answer a statistical question has a distribution which can be described by its center, spread, and overall shape. Additionally, students collect these data using base tens (x10 lux).

The following math concept will be useful in explaining why they are selecting this setting on the light sensors.

  • CCSS.Math.Content.5.NBT.A.1: Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represents in the place to its left.

Consult with your students’ math teacher(s) prior to Lesson 3 to coordinate your approach to the math concepts listed above with what your students will experience in their math classes.

How do I shorten or condense the unit if needed? How can I extend the unit if needed?

The following are example options to shorten or condense parts of the unit without eliminating important sensemaking for students:

  • Lesson 1 and 2: There is an extended self-documentation activity that is introduced in Lesson 1 and revisited 3 times in Lesson 3. This is to build a documentation board of related experiences. This activity can be cut out and the use of a shorter related phenomenon chart could be used instead, which is also included in Lesson 1.
  • Lesson 3: The lab investigation in this lesson could be completed as a demonstration lab in a Scientist Circle to get a class set of data for small group analysis.
  • Lesson 6: The investigation with flashlights and convex lenses could be cut out or changed to a brief demonstration.
  • Lesson 8: This entire lesson could be shortened to only test glass in the box model with collaborative sense-making of what was observed, followed by the final transfer task assessment.


The following are example options to extend parts of the unit to deepen students’ understanding of science ideas:

  • Lesson 6: The refraction Extension Opportunity will allow students to develop a more robust understanding of how light bends (or changes direction) when it encounters different transparent mediums (air, water, glass).
  • Lesson 8: The scattering Extension Opportunity allows students to explain more fully why certain smooth surfaces result in a mirror reflection compared to bumpier surfaces.
What are recommended adult-level learning resources for the science concepts in this unit?

The OpenSciEd instructional model focuses on the teacher being a member of the classroom community, supporting students to figure out scientific ideas motivated by their questions about phenomena. Students iteratively build their understanding of phenomena as the unit unfolds. To match the incremental build of a full scientific explanation across the unit, the science content background necessary for you to teach individual lessons incrementally builds too. Throughout the unit, we provide just-in-time science content background for you that is specific to the Disciplinary Core Ideas (DCIs) that will be figured out in a lesson. Places to look for this guidance include the “Where we are going” and “Where we are not going” sections for each lesson. Also, the expected student responses, keys, and rubrics illustrate important science ideas that should be developed in each lesson. The K-12 Science Framework is another great resource to learn more about the DCIs in this unit (PS4.B and LS1.D), including what students have learned previously and where they are headed in high school.


In addition to the science content background information embedded in the lesson resources, below we provide recommended resources that can help build your understanding of phenomena and Performance Expectations bundle for this unit:


  • Fortus, D., & Krajcik, J. (2017) Chapter 5, Core Idea PS4: Waves and Their Application for Technologies in Information Transfer. In Duncan, Kracjik, and Rivet (Eds)., Disciplinary Core Ideas: Reshaping Teaching and Learning. Arlington, VA: NSTA Press. https://my.nsta.org/resource/105601/disciplinary-core-ideas-reshaping-teaching-and-learning 
  • Paul Anderson at Bozeman Science has produced additional informational videos on the NGSS Disciplinary Core Ideas focused on in this unit.

For more information about one-way mirror technology, read about and watch How do one-way mirrors work? at https://science.howstuffworks.com/question421.htm and  https://www.youtube.com/watch?v=4kKL32opewI&t=38s 

Unit Acknowledgements
Unit Development Team
  • Lindsey Mohan, Unit Lead, BSCS Science Learning
  • Zoe Buck Bracey, Writer, BSCS Science Learning
  • Emily Harris, Writer, BSCS Science Learning
  • Audrey Mohan, Writer, BSCS Science Learning
  • Tracey Ramirez, Writer, The Charles A. Dana Center, The University of Texas at Austin
  • Abe Lo, Reviewer, PD design, BSCS Science Learning
  • Michael Novak, Conceptual design, Northwestern University
  • Misty Richmond, Pilot Teacher, James Ward Elementary School, Chicago Public Schools
  • Ty Scaletta, Pilot Teacher, Alcott College Prep Elementary School, Chicago Public Schools
  • Keetra Tipton, Pilot Teacher, Aptakisic Junior High School, Buffalo Grove, IL
  • Katie Van Horne, Assessment Specialist, Concolor Research
  • David Fortus, Unit Advisory Chair, Weizmann Institute of Science
  • Susan Gomez-Zwiep, Advisory Team, BSCS Science Learning
  • Dominique Poncelet, Advisory Team, Southeast Middle School, Oklahoma City Public Schools
Production Team

BSCS Science Learning

  • Maria Gonzales, Copyeditor, Independent Contractor
  • Kate Herman, Copyeditor, Independent Contractor
  • Stacey Luce, Copyeditor and Editorial Production Lead
  • Renee DeVaul, Project Coordinator and Copyeditor
  • Valerie Maltese, Marketing Specialist & Project Coordinator
  • Chris Moraine, Multimedia Graphic Designer
  • Kate Chambers, Multimedia Graphic Designer
Unit External Evaluation
NextGenScience’s Science Peer Review Panel

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by NextGenScience’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has earned the highest score available and has been awarded the NGSS Design Badge. You can find additional information about the EQuIP rubric and the peer review process at the nextgenscience.org website.