Unit 04 · Designing a Controlled Experiment
This is where the whole method comes together: a fair test that can actually tell you something. A student changes one thing on purpose, holds everything else steady, and compares against a baseline — does the bean seedling grow taller under the lamp or by the window, and how do you know it was the light and not the water? This skill sits after measurement because a controlled experiment is only trustworthy when the numbers are. Mastery means you can design a test whose result no one could wave away.
| Criterion | Developing | Proficient | Mastery |
|---|---|---|---|
| Independent & dependent variables | Cannot say what is being changed or what is being measured. | Names one but mixes up which is changed and which is measured. | Names the one thing changed on purpose (lamp vs. window) and the one thing measured (seedling height), clearly and out loud. |
| Controlled variables (fair test) | Changes factors without tracking their effects. | Controls some conditions but overlooks a plausible confounder. | Controls relevant conditions, identifies remaining variation or confounders, and explains how the design strengthens but does not guarantee a causal inference. |
| Control / comparison group | Runs only the test condition, with nothing to compare it to. | Knows a comparison is needed but sets up one that is not a fair baseline. | Defines an appropriate comparison group and explains its similarities, differences, and allocation; does not assume organisms are identical. |
| Replication & sample size | Tests one seedling once and calls it settled. | Runs a couple of trials but too few to trust, or cannot say why more would help. | Plans enough seedlings and repeats to tell a real effect from a fluke, and explains why the number matters. |
| Procedure clarity | Keeps the plan in their head; written steps are vague or missing amounts. | Writes steps but leaves out a measurement, timing, or detail a stranger would need. | Writes a procedure clear and complete enough that another person could run the exact experiment without asking a question. |
| Integration (cross-domain) | Makes no supported connection between the source and the science. | Uses the source but needs help connecting evidence, writing, or limitations to the science. | Independently connects History, Reading, and Writing using a cited source, appropriate evidence, a limitation, and a scientific explanation. |
Integration is reported separately and cannot lower the science grade or block a science demonstration pass. Science and practical criteria determine that pass. Use the integration guide's evidence checklist for the separately reported criterion.
“The one thing I’m changing is light — lamp versus window — and I’m measuring how tall each seedling gets. Everything else stays the same: same soil, same water, same pot. I’ll grow four under each so one weird plant can’t fool me, and I’ll keep a control on the counter to compare against.”
“I’ll put one by the window and give it more water and better soil and see if it grows. Just the one plant. If it’s taller, the window worked.”
You demonstrate this unit through watched design tasks — planning and setting up a fair test at the bench — plus short oral checks where you defend your choices aloud. Not a multiple-choice test. A criterion counts as mastered only when a guide can watch you do it: change one variable, control the rest, build in a comparison, and write steps another person could follow. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.