Sequencing topics to…

…create cognitive conflict.

Hello all. Welcome to the 172nd edition of TEPS Weekly!

A group of Grade 8 Science teachers are planning a unit on astronomy. The unit includes three closely related topics: the Moon, phases of the Moon, and eclipses. The textbook places them in that order. The yearly plan places them neatly in the same term. On paper, the sequence looks simple: teach the Moon, teach phases, and then teach eclipses.

One teacher says, “The textbook has Moon phases before eclipses, so let us follow that order.”Another teacher says, “But eclipses are more exciting. If we start with an eclipse, students will be hooked immediately.”A third teacher pauses and says, “I am worried about starting with eclipses. Eclipses bring in the idea of Earth’s shadow. If students do not yet understand Moon phases, they may start using the same shadow idea to explain why the Moon looks different across the month.”

These points change the direction of the discussion. The teachers are no longer asking, “What comes next in the textbook?” They are asking, “What idea must students understand first, so that the next idea does not get misunderstood?” or “What sequence makes it easy for students to understand each of these ideas?” Textbook order arranges content. Learning sequence arranges understanding.

Sometimes the printed order works well. Sometimes it needs a bridge or rearrangement. In this case, the teachers need to decide how students should build the idea in their minds:

1. What makes these topics difficult to understand?

2. What prior information or experience can the students leverage to understand this topic better?

3. Can I start with a simple example and move to make a general principle?

Moon phases and eclipses both involve the Sun, Earth and Moon, but they work in different ways. In Moon phases, the Moon appears to change shape because we see different portions of its sunlit half. In a lunar eclipse, Earth’s shadow falls on the Moon. The difficulty is that students may not see this difference clearly.Students do not come to this topic with an empty mind. They have seen crescent Moons, half Moons and full Moons. From their day-to-day experiences, they know that shadows make things dark. They may also have heard that eclipses involve Earth’s shadow. This is their prior knowledge: what they already know or believe before the lesson begins.

But prior knowledge does not stay as separate facts in students’ minds. Students use it to build explanations, and those explanations shape how they understand the next idea. This is useful for learning. However, if students have a misconception and they link the new idea to the wrongly held prior knowledge, it can mislead them. For example,  in the case of Moon phases, students may see one part of the Moon bright and another part dark. They may connect this with what they know about shadows and form a mental model: ‘Earth’s shadow must be covering the Moon’. A mental model is the explanation students use to make sense of something.

That is what makes the topic tricky. The shadow idea is correct and is useful in the context of eclipses, but may become a hindrance in the context of phases of the Moon. 

So the real question is not, “Should eclipses come before phases or after phases?”

The better question is, “How can understanding of an eclipse help students understand before they learn Moon phases?”

The case for the eclipse to phases sequence

Concrete vs. Abstract

An eclipse is a concrete event. It is easier to picture. In a lunar eclipse, the Sun, Earth and Moon line up, and Earth’s shadow falls on the Moon. This is a clear example of a shadow event.

Secondly, an eclipse is based on very basic prior knowledge:

1. Light travels in a straight line

2. An opaque object in the path of light causes a shadow

Thirdly, eclipses can be easily understood through a demonstration using a ball and a torch.

Understanding of Moon phases is more abstract and more difficult to imagine. Nothing is covering the Moon. The Moon is not changing shape. Students have to not only understand the perspective of the light coming from the Sun (not from where they are viewing it) and then imagine the Moon reflecting the sunlight to us on the Earth. 

So, in this case, starting with an eclipse can make sense – not because it is exciting, but because it is concrete. It can help students first see the contrast between an eclipse and Moon phases, before they later connect both ideas as part of the Sun-Earth-Moon system.

Cognitive Conflict

If students first understand what a real shadow event looks like, they can also begin to see why Moon phases are definitely not shadow events. In a lunar eclipse, Earth’s shadow falls on the Moon only when the Sun, Earth and Moon are positioned in a very specific straight line. This alignment is rare – usually, only about two lunar eclipses happen in a year on Earth. But Moon phases happen regularly across the year, while the Sun, the Moon and the Earth aligning in a straight line does not happen that often. Alternatively, if Moon phases were caused by Earth’s shadow, then there would be a lunar eclipse every month. 

And this brings us to the fourth reason for teaching eclipse before phases of the Moon: cognitive conflict. We wrote earlier about misconceptions that students may have about phases of the Moon – shadows cause phases. But using this approach where we use the shadow of the Earth to speak about the eclipse, and then show them that the Earth is not in the way of the Sunlight going toward the Moon, it creates a conflict with the students’ mental model. This conflict is called a cognitive conflict, and this is a very useful approach to ensure deeper understanding in students. It does not simply tell students that their idea is wrong. It helps them test their own explanation. At first, “the dark part is Earth’s shadow” may feel sensible to students because they know shadows make things dark. But when they see that Earth’s shadow falls on the Moon only during a special eclipse alignment, they realise that the same explanation cannot work for Moon phases that change regularly across the month.

This gap makes students pause and rethink. They now have a reason to look for a better explanation. When the teacher then introduces the idea that the Moon reflects sunlight and we see different portions of its sunlit half, students are not just memorising a new fact. They are replacing an earlier explanation with a stronger one. It helps students notice the limit of their existing idea, compare it with evidence, and build a more accurate mental model.

So how did we decide the sequence of topics?

Here, the learning problem is that students may wrongly use shadow to explain Moon phases. So the sequence can first make the shadow idea clear through eclipses, then show its limit, and only then build the idea of Moon phases. We can do the same for other topics, as well.

In force and motion, students may think a moving object needs a continuous force to keep moving. 

• Concept clarity: Build friction as a force that acts against motion. This helps students see why moving objects around us usually slow down or stop.

• Limit: If friction stops motion, why does a puck slide farther on ice than on rough ground?

• Conflicting idea: If less friction means motion for a longer distance, then to move something, we do not need a continuous force on it. A force is needed to change motion, not to keep motion going.  

In plant nutrition, students may think plants get food from the soil. 

• Concept clarity: Build the idea that plants take in materials from their surroundings. This helps students see that plants get water and minerals from the soil, and carbon dioxide from the air.

• Limit: Of these materials – water, minerals and carbon dioxide – which ones come from the soil? That means soil does not make the food for plants.

• Conflicting idea:  If soil gives only some materials, then plants do not get food directly from the soil. They make food through photosynthesis, using water, carbon dioxide and sunlight to produce glucose.

In each case, students already have an explanation in their minds based on their prior knowledge and mental model. The learning sequence has to work with that explanation, not ignore it. And in most cases, use it to create a cognitive conflict to ensure deeper student understanding.

That is why curriculum or teaching planning should not move straight from the chapter list to the calendar. Teachers do not have to choose the order only by textbook sequence or by which topic feels most exciting. The chapter list gives the content. The calendar gives the timeline. But the learning sequence decides how students’ understanding should grow.

Before finalising the order, the teachers need to ask: What makes these topics difficult to understand? What prior information or experience can the students leverage to understand this topic better? Can I start with a simple example and move to make a general principle?

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Edition: 5.27