Bean Plants, No Windows, Locked Building
Ms. Brennan's first-grade class of 24 is starting a three-week plant unit. On the pre-assessment, 17 of 24 children wrote or drew that plants get their food from soil, and several said roots 'drink dirt.' The district kit supplies only bean seeds, paper cups, and potting soil. Her classroom has no windows; the nearest daylight is a hallway 40 meters away, and the building is locked on weekends. The principal requires that anything alive in the room survive unsupervised from Friday afternoon to Monday morning. Ms. Brennan wants children to move beyond reciting that plants need light and to be able to point to evidence.
1. Design a fair test that fits the constraints (no windows, locked building on weekends). What can it show, and what can it not show?
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Set up 12 matched cups, six seeds each or one seedling per cup, same potting soil, same watering, same seed type, placed on one shelf. Set the variable: six cups under a grow lamp on a 12-hour timer, six in a sealed cardboard box with a small vent hole, same room temperature. The comparison is one difference, which is what makes it fair at first grade.
Weekend survival: water heavily on Friday and run a cotton wick from a cup of water into each cup, or place cups in a shallow tray with 2 cm of water, and test that setup for two days before committing. Put the grow lamp on a timer so it does not depend on anyone being in the building.
What it can show: light affects color, leaf size and number, and stem sturdiness. What it cannot show: that plants make their own food, or that soil is not food. It also has a built-in trap. Bean seedlings in the dark typically grow taller and paler, so children may read 'dark is better.' Plan the measures in advance, height plus color plus leaf count plus stem firmness, and have children record all four rather than height alone. Three weeks is enough for germination and visible contrast, not for lifecycle claims.
2. What questioning sequence would surface and confront the 'food from soil' idea without simply telling children they are wrong, and what evidence would actually be needed?
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Start by making the idea public and respectable, because 17 of 24 hold it. Chart predictions: 'If soil were the plant's food, what would we see happen to the soil?' Then test the prediction in a way first graders can actually observe.
Two probes work. First, mark the soil level in each cup with a line and a date, then re-measure weekly. If plants were consuming soil, the level would drop. It does not, and the children can see that with their own data. Second, ask what the roots are doing if not eating: pull one spare seedling and look at how soil clings to the roots, and discuss anchoring and water.
Ask 'where does the plant's mass come from?' only as a wonder question, not an assessable one; the answer is far above grade level. Keep the target at what evidence supports at grade 1: plants need light and water to grow and stay healthy, and soil holds the plant and supplies water.
Close each session with a revision prompt: 'What do you think now, and what made you change your mind?' The reasoning is the point, not the slogan.
3. How should Ms. Brennan assess whether children can explain rather than recall, given three weeks and 24 children?
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Use a short structured interview plus a drawing, not a vocabulary quiz. Over three days, pull five or six children at a time during center work while the rest do observation-journal entries; each interview takes about three minutes.
Task: 'Draw our two sets of cups. Which ones got light? What happened? Why do you think so?' Then two follow-ups: 'What would happen if we put both sets in the dark?' and 'What does the soil do for the plant?' Score on a three-level rubric: Level 1 names an observation only; Level 2 links light or water to the observed difference; Level 3 links both and cites a specific observation from the class data, such as the pale color or the unchanged soil line.
Explicitly accept 'plants need light and water to grow' as meeting the standard. Do not require the phrase about making food; that is beyond first grade and would push the assessment back toward recitation.
Compare each child's interview drawing to their pre-assessment drawing and keep both in the portfolio, so growth in explanation is visible without a written test. Children who still insist soil is food after the evidence should be re-interviewed rather than marked wrong, since the goal is revision over time.