Evaluating Solutions — Evaluate solutions using evidence. - 3rd Grade Science

SECTION 1

Why Do We Need to Evaluate Solutions?

People have always tried to solve problems in nature. Sometimes a farmer needs to keep bugs away from crops. Sometimes a town needs to help animals cross a busy road safely. But here is the big question: how do we know which solution actually works? That is where evaluating solutions using evidence comes in!

Over many years, scientists and problem-solvers learned that guessing is not enough. They discovered that you need real facts — called evidence — to figure out if a solution is truly helping. Let's look at some important moments in history when people started using evidence to evaluate their ideas.

1800s • Farmers Test Crops

Farmers began planting different types of seeds side by side to see which ones grew better. They used what they saw — the evidence — to pick the best crops.

1900s • Wildlife Refuges Created

People noticed that some animals were disappearing. They collected evidence about animal populations and created safe spaces called wildlife refuges to protect them.

1970s • Endangered Species Act

Scientists used evidence about shrinking animal populations to convince lawmakers to pass a law that protects endangered animals.

Today • Evidence-Based Problem Solving

Today, scientists test many solutions and compare the results before deciding on the best one. This is called evaluating solutions using evidence!

So the big question this lesson answers is: How do we use evidence to decide if a solution really helps living things survive?

SECTION 2

Core Principles of Evaluating Solutions

Before we can evaluate a solution, we need to understand a few important ideas. Think of these as the rules of the game. When scientists want to know if a solution works, they follow these steps carefully.

Identify the Problem

First, you need to clearly understand the problem. What is happening to the living things? Why do they need help? For example: "Frogs are disappearing from the pond."

Look at the Solution

Next, look at the solution someone has come up with. What is it supposed to do? A solution might be: "Build a small fence around the pond to keep predators out."

Gather Evidence

Evidence means facts and observations. You count, measure, and observe. Did the number of frogs go up after the fence was built? That is evidence!

Compare and Decide

Compare what happened before and after the solution. If the evidence shows the solution helped, it is a good one! If not, we try something different.

Share Your Findings

Scientists always share their evidence with others. This way, everyone can learn from the results and agree on the best solution.

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KEY TAKEAWAY

Think of evaluating a solution like taste-testing two recipes for cookies. You would not just guess which recipe is better — you would bake both, taste them, and use what you actually taste (the evidence) to decide which one is yummier. Scientists do the same thing with their solutions — they test and observe before deciding!

SECTION 3

How Evaluating Solutions Works — A Visual Guide

Let's look at a diagram that shows the steps of evaluating a solution. Follow the arrows from the problem all the way to the decision. This is how real scientists think!

This flowchart shows how scientists evaluate solutions. Notice how if the evidence shows the solution is not working, the red dashed arrow loops back to try a new solution. This is called iterating — it means trying again!

In the diagram above, you can see how each step builds on the one before it. The most important step is gathering evidence. Without evidence, you are just guessing. With evidence, you can make a smart decision about whether a solution is helping living things or not.

SECTION 4

How Evidence Helps Living Things Survive

In nature, living things face many challenges. Some animals might lose their homes when trees are cut down. Some plants might not get enough water. When people want to help, they come up with solutions. But how do we know the solution is actually helping? We look at the evidence!

What Counts as Evidence?

Evidence is information that you can see, count, or measure. It is not a feeling or a guess. Here are some examples of evidence that scientists use when they evaluate solutions for helping living things.

✓ Counting animals — Did the number of birds in the park go up or down after we added birdhouses?
✓ Measuring plant growth — Did the plants grow taller after we changed the type of soil?
✓ Observing behavior — Did the turtles start using the new crossing tunnel under the road?
✓ Taking photographs — Do before-and-after photos show more trees growing in the area?

Why Evidence Matters for Living Things

Living things depend on their environment (the place where they live) to survive. When the environment changes, some living things might not survive. By using evidence to evaluate solutions, we can figure out the best way to help them. If a solution is not working, the evidence tells us to try something new. If a solution is working, the evidence tells us to keep going!

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Think About It

Imagine you plant flowers to help bees in your schoolyard. After one month, you count the bees. If you see more bees than before, that is evidence your solution is working. If you see the same number or fewer bees, you might need to try a different kind of flower!

SECTION 5

Real Examples — Evaluating Solutions for Animals and Plants

Let's look at a real-world example. In many places, animals like deer, frogs, and turtles need to cross roads to find food or water. Cars can be very dangerous for them. People came up with different solutions and used evidence to figure out which ones actually helped.

This diagram compares three different solutions for helping animals safely cross a road. By counting the number of animals hurt before and after each solution, scientists collected evidence. Solution B (the underground tunnel) had the best evidence — it reduced the number from 20 to only 3!

As you can see, all three solutions helped a little bit. But the evidence — the actual numbers — showed that the underground tunnel helped the most. That is why evaluating solutions using evidence is so important. Without counting and comparing, we might have just guessed that the warning signs were enough!

SECTION 6

Worked Example — Helping Butterflies in the Schoolyard

Let's walk through a complete example together. Imagine your class wants to help butterflies visit the schoolyard more often. You come up with two solutions and need to evaluate them using evidence.

Which Solution Brings More Butterflies?

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Step 1 — Identify the Problem

Your class notices that very few butterflies visit the schoolyard. You count the butterflies every day for one week and find an average of 2 butterflies per day. You want more butterflies to come!

Problem: Only 2 butterflies per day visit the schoolyard.
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Step 2 — Look at the Solutions

Your class comes up with two solutions. Solution A: Plant a butterfly garden with colorful flowers. Solution B: Put out a dish of sugar water for the butterflies.

Two solutions to test: butterfly garden and sugar water dish.
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Step 3 — Gather Evidence

You try both solutions at the same time. Every day for two weeks, you count the butterflies near the garden and near the sugar water dish. Here is what you found: The butterfly garden attracted an average of 8 butterflies per day. The sugar water dish attracted an average of 4 butterflies per day.

Evidence: Garden = 8 butterflies/day; Sugar water = 4 butterflies/day.
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Step 4 — Compare and Decide

Before either solution, you had 2 butterflies per day. The garden brought 8 butterflies per day — that is 6 more than before! The sugar water brought 4 per day — that is only 2 more. The evidence shows that the butterfly garden is the better solution because it attracted more butterflies.

Winner: The butterfly garden! It brought 6 more butterflies per day (compared to 2 more for the sugar water).
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Step 5 — Share Your Findings

You share your results with other classes. You explain the numbers you collected and why the garden worked better. Now the whole school knows what the evidence says!

Sharing evidence helps everyone learn and make better decisions.

SECTION 7

Strengths and Limitations of Different Types of Evidence

Not all evidence is the same. Some types of evidence are stronger than others. Let's compare the different kinds of evidence you might use when evaluating a solution.

Type of Evidence	Strengths	Limitations
Counting (numbers)	Very clear and easy to compare. Numbers do not lie!	You might miss some animals or plants when counting.
Photographs	You can see changes over time. Great for showing others.	A photo only shows one moment. It might not tell the whole story.
Observations (watching)	You can notice details that numbers might miss, like animal behavior.	Two people might see things differently. It can be less exact.
Measurements (ruler, scale)	Very precise and scientific. Easy to repeat.	You need the right tools and need to measure carefully.

Comparing different types of evidence

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KEY TAKEAWAY

Using evidence to evaluate solutions is like being a detective. A detective does not solve a mystery based on a hunch — they collect clues (evidence!) and look at all of them together. The more types of evidence you collect — counting, photos, observations — the stronger your case. The best scientists use multiple types of evidence to make the best decision.

SECTION 8

From Evaluating Solutions to Designing New Ones

Right now, you are learning how to evaluate solutions — that means judging whether they work. As you grow older as a scientist, you will also learn how to design your own solutions from scratch. Let's compare what you are learning now with what comes next.

What You Are Learning Now	What Comes Next
You look at solutions that others created.	You will create your own solutions to new problems.
You collect evidence to see if a solution works.	You will design experiments to test your own ideas.
You compare two or three solutions.	You will combine the best parts of many solutions into one.
You share findings with your class.	You will write scientific reports and present to larger groups.

Your science skills now vs. in the future

The skills you are building now — collecting evidence, comparing results, and making decisions based on facts — are the same skills that real scientists and engineers use every single day. You are already thinking like a scientist!

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Fun Fact

Engineers who build bridges, design video games, or even plan zoos all evaluate their solutions using evidence before they finish a project. They test, measure, and improve — just like you are learning to do!

SECTION 9

Practice Problems

Now it is your turn! Try these practice problems. Think carefully about the evidence before you answer.

Question 1: CONCEPTUAL

What is evidence? In your own words, explain why scientists use evidence instead of just guessing when they evaluate a solution.

Show answer

Evidence means facts, numbers, or observations that you can see and measure. Scientists use evidence instead of guessing because evidence tells you what is actually happening. A guess might be wrong, but if you count 10 more birds after building a birdhouse, that number is real proof that the solution is working. Evidence helps us make fair and smart decisions.

Question 2: BASIC CALCULATION

A class planted wildflowers to help bees. Before planting, they counted 5 bees per day. After planting, they counted 12 bees per day. How many more bees came after the flowers were planted? Does the evidence show the solution worked?

Show answer

There were 12 − 5 = 7 more bees per day after the flowers were planted. Yes, the evidence shows the solution worked! The number of bees went up by 7, which means the wildflowers attracted more bees to the area. Since the number increased, the evidence supports the idea that planting wildflowers is a good solution for helping bees.

Question 3: INTERMEDIATE

A park ranger tried two solutions to help fish in a stream. Solution A: Remove trash from the water. After one month, there were 15 fish. Solution B: Plant trees along the stream for shade. After one month, there were 22 fish. Before either solution, there were 10 fish. Which solution does the evidence support more, and why?

Show answer

The evidence supports Solution B (planting trees) more. With Solution A, the fish went from 10 to 15, which is 5 more fish. With Solution B, the fish went from 10 to 22, which is 12 more fish. Since Solution B resulted in 12 more fish compared to only 5 more for Solution A, the evidence shows that planting trees helped the fish population more. The shade from the trees may have kept the water cool, which many fish prefer.

Question 4: APPLIED

Your town wants to help sea turtles reach the ocean safely after hatching on the beach. Someone suggests turning off bright lights near the beach at night because baby turtles follow light and might walk toward street lights instead of the ocean. What evidence would you collect to evaluate if this solution works? Describe at least two types of evidence.

Show answer

You could collect at least two types of evidence. First, you could count the number of baby turtles that successfully reach the ocean each night, both before and after turning off the lights. If more turtles reach the ocean after the lights are turned off, that is strong numerical evidence. Second, you could observe and record the direction the baby turtles walk. Before turning off lights, you might see some walking toward the street. After turning off lights, you should see more walking toward the ocean. You could also take photographs or videos to show the difference in turtle behavior.

Question 5: CRITICAL THINKING

A student says, "I think putting a scarecrow in the garden will keep rabbits away from the lettuce." After one week, there are fewer bite marks on the lettuce. Another student says, "Wait — it also rained a lot this week, and rabbits do not like rain." How does this affect the evaluation? Can you be sure the scarecrow is the reason? What would you do to get better evidence?

Show answer

This is a tricky situation! The rain could be the real reason the rabbits stayed away, not the scarecrow. When two things change at the same time, it is hard to know which one caused the result. This is why scientists try to change only one thing at a time. To get better evidence, you could wait for a dry week and see if the scarecrow still keeps the rabbits away. You could also try two garden beds — one with a scarecrow and one without — during the same week. If the bed with the scarecrow has fewer bite marks, that is stronger evidence that the scarecrow is helping. This is how scientists make their evidence more reliable.

SUMMARY

Lesson Summary

Summary

In this lesson, you learned how to evaluate solutions using evidence. You discovered that evidence means real facts, numbers, and observations — not just guesses. You learned the five key steps: identify the problem, look at the solution, gather evidence, compare results, and share your findings.

You also saw real examples of how people use evidence to help living things survive, like building animal crossing tunnels and planting butterfly gardens. You learned that the best evidence comes from counting, measuring, observing, and photographing. Remember: the more evidence you collect, the better your evaluation will be. You are already thinking like a real scientist!