Lesson Q1 L1 – Control Group Experiments

Lesson Overview

Quarter 1 · Unit 1: The Control-Group Experiment · Week 1 · Grades 9–12 · Lesson length: 45 minutes

Essential Question: How can we tell whether a change we make actually causes a result?

Lesson Focus: A farmer adds composted manure, and the lettuce looks great. Did the manure do it?

Why It Matters: This lesson launches the SSS challenge. Students learn what makes an experiment (we change something on purpose) and why a control group is the only way to know whether the change caused the result. These ideas drive every lesson that follows.

Teacher Note: This lesson keeps the authors’ examples: the manure-and-lettuce scenario, the fair race, the Drug X thought experiment, DRY-MIX, and the vitamin C assessment task. See the Teacher Background primer (front matter) for the research on the control-of-variables strategy.

Source: Rewritten from the SSS book — SSS book, Lesson Plan 1 and Chapter 2 primer.

Standards & Learning Targets

Standards Alignment

NGSS Science & Engineering Practices: Asking Questions; Planning and Carrying Out Investigations. Crosscutting Concepts: Cause and Effect.

ISTE Standards for Students: 1.3 Knowledge Constructor (1.3d: build knowledge by exploring real-world issues and problems).

Student Learning Targets

Learning Targets — students will be able to

• Define an experiment and explain why the researcher must change something on purpose.

• Explain the role of a control group and identify the independent and dependent variables in an example.

• Describe how agricultural experiments support innovation, sustainability, and food security, and describe the SSS challenge.

Key Vocabulary

experiment · control group · treatment group · independent variable · dependent variable · fair test · sample size · hypothesis

Materials & Teacher Prep

Materials Needed

• Science notebooks (garden/lab journals)
• Image of an agricultural control-group plot (Appendix A) or a photo of a local test plot
• Chart paper and markers for each team
• Student Workbook page 1.1

Teacher Prep Checklist

• Write the SSS challenge on the board: “With a partner you will get one square foot of growing space and radish seeds. Design and conduct a control-group experiment.”
• Prepare the lettuce scenario and the DRY-MIX chart.
• Form partners and teams of four (two pairs) for the year.

Safety: Use only fully composted, bagged manure products; gloves on and wash hands afterward. Sources: EPA, Approaches to Composting; ADHS, School Garden Program. See the Safety & Fact-Check Log.

Lesson Flow & Timing

Phase 1 · Engage — The Hook

Teacher Talk

PCM: Curiosity. “Today we begin an exciting project. With a partner you will receive a one-square-foot growing area and radish seeds, and you will design and conduct a controlled experiment.” Then tell the scenario: a field gets composted manure and grows lettuce. After seven weeks the lettuce is a perfect shade of green and the average mass is 300 grams. “What can we conclude?” Preview the vocabulary this task depends on: experiment. Formal definition follows in Explain.

Ask Students

“What is an experiment? How is it different from just doing a lab activity?” “Could the lettuce have grown just as well without the manure? How would we know?” “What would be a good comparison group for this field?”

PCM Differentiation

Thinker Students: “Name every factor besides manure that could explain the 300 grams. Which ones would you have to keep the same?”

Harmonizer Students: “Farmers spend money and time on manure. Why would a farming family want to know for sure that it works?”

Phase 2 · Explore — Kagan Cooperative Activity

Cooperative Structure

Kagan structure: Numbered Heads Together. Numbered Heads Together fits because every team member must be able to explain the team’s experimental design; any number can be called to share. (See the Teaching Reference for the structure’s steps.) Flag control group, independent variable, dependent variable, fair test, and sample size as students begin; they will hear them defined in Explain.

Step-by-Step

• Step 1 — Fair race warm-up (3 min): “I want to race two students to see who is faster.” Teams list what must stay the same for a fair test (distance, start time, shoes). Establish: only the runner (independent variable) changes; the time (dependent variable) is measured.

• Step 2 — Think and write alone (3 min): Pose the thought experiment: “Design an effective experiment to find out if Drug X helps people recover from lung cancer.” Each student writes an independent variable, a dependent variable, and a control group.

• Step 3 — Heads together (7 min): Teams agree on one design and make sure every member can explain it. Guiding questions: What is your independent variable? Dependent variable? Control group? How many people will be in your study?

• Step 4 — Numbers called (4 min): Call a number (for example, “Person 3”) from three teams to share designs. Discuss sample size: larger samples give more confidence and statistical power but cost more time and money, so researchers balance them.

Teacher Moves During Explore

• Listen for designs without a control group and ask, “Compared with what?”

• Push for one independent variable: “If you change the drug and the diet, what caused the change?”

• Raise fairness to people: control groups in medicine get a placebo or the standard treatment.

Phase 3 · Explain — Direct Instruction

Mini-lesson — Experiments, Controls, and Variables. Teacher move: Pull the vocabulary out of the student designs and connect to agriculture, then write experiment, control group, and independent vs. dependent variable on the board with one garden example each for students’ notebooks.

• Experiment: A procedure in which one or more variables are changed on purpose to see the effects on other variables. If nothing is changed, it is an observation, not an experiment.

• Why experiment: To (a) test hypotheses and (b) establish cause-and-effect relationships.

• Control group: The comparison group that does not get the treatment but is otherwise the same. The group that gets the treatment is the treatment group. In the lettuce case, a control field without manure would show whether manure made the difference.

• Independent vs. dependent variable: The independent variable is what I change (the manure). The dependent variable depends on it and is what we measure (plant health and mass). Memory tip: DRY-MIX — Dependent, Responding, Y-axis; Manipulated, Independent, X-axis.

• Experiments in agriculture: Experiments drive innovation, sustainability, and food security: neem oil can treat pests with less harm to beneficial insects; research helped eradicate the pink bollworm, a 100-year cotton pest; Arizona’s Agricultural Experiment Stations began in the 1890s (today in Tucson, Maricopa, Safford, and Yuma) and test citrus, vegetables, cotton, grasses, and forage crops.

Key Message: An experiment changes one thing on purpose and compares the result to a control group. Without the control, we cannot say what caused the result.

Check for Understanding — Ask Students

“What is the independent variable in the manure-and-lettuce experiment?” “Why is a control group needed?” “Why are experiments important in agriculture?”

Phase 4 · Elaborate — Student Product & Differentiation

Student Product

Students restate the SSS challenge in their notebooks and label the independent variable, dependent variables, and control group for one agricultural example of their choice (fertilizer, mulch, or shade).

Differentiation (Grades 9–12)

Scaffolded support: Use the frame “If I change ___, I will measure ___, and my control group will be ___.” Label one example from the lesson, then one of your own.

Grades 9–12: Standards Amplification (HS.L2U3.18): explain how a treatment is a human intervention in an agricultural ecosystem. Compare monoculture and diverse plantings: lower biodiversity can raise pest risk. Note one economic or political factor in agricultural research funding.

Phase 5 · Evaluate — Closure, Exit Ticket & Assessment

Exit Ticket

1. What is an experiment?

1. Why is a control group needed?

1. Design an experiment to see if vitamin C supplements reduce the number of times someone gets sick in the winter months. Name the independent variable, dependent variable, and control group.

Answer Key / Look-Fors: (1) A procedure where the researcher changes one variable on purpose to see its effect on another. (2) It gives a comparison so we can tell whether the treatment caused the result. (3) IV: taking vitamin C (yes/no); DV: number of illnesses in winter; control: a similar group given a placebo; strong answers mention a large sample and keeping other factors the same.

Expanding Circles

How does this connect to… Self — What is a claim you have heard (an ad or a video) that needs a control group? • Classroom — How will our class make every radish test a fair test? • School — What school decision could be tested with a control group? • Community — Why do Arizona farmers rely on experiment station results? • World — How do control-group experiments improve food security worldwide?

Formative Assessment

Formative Assessment (to sort students, use the labeled independent, dependent, and controlled variables in each notebook and the exit-ticket vitamin C experiment design)

• Meets (3): Correctly identifies IV, DV, and control in the vitamin C design and explains why the control matters.

• Approaching (2): Identifies the variables but the control group is missing or not comparable.

• Not Yet (1): Cannot separate the variables — reteach with the fair race example and the DRY-MIX chart before Lesson 1.2.

Extend & Looking Ahead

• Extension: Students find a product claim online and ask, “Where is the control group?” (Koch, 2021, and Tanner et al., Oregon State Extension EM9381, are teacher references from the original lesson.)

• Looking Ahead: Lesson 1.2 presents the challenge in full and partners choose the variable they will test.