Lesson plan Grade 2 Science
Road Salt at Rowanwood School: A Grass Seed Water Test
A five-day grade 2 investigation comparing grass seed watered with plain water against seed watered with salty water, matched to the brown strip beside a road.
Objectives
- Students will set up two seed trays that differ in only one thing.
- Students will record what each tray looks like on four days in a row.
- Students will explain why the grass beside a salted road turns brown.
Vocabulary
Key words: seed, sprout, salt, runoff, fair test, record
Teacher overview
Rowanwood Street is fictional, and it stands for the salted road beside almost any northern school, where every spring a brown strip appears in the grass along the curb while the rest of the yard greens up. This lesson turns that strip into a testable question by giving two trays of grass seed the same light and the same daily amount of water and changing only whether that water is salty. Students commonly explain the brown strip as cold damage or as plow damage, which is why the two trays must sit side by side in the same window, both watered, so that neither cold nor thirst can account for the difference. The investigation runs across five short sessions, with the first and the last taking most of the time.
Procedure
Hook, day 1 (5 min): Describe the strip of brown grass along Rowanwood Street each April, with green grass a few steps farther in. Ask: "Both patches got the same rain and the same sun. Why would only one turn brown?" Take three guesses and write them where the class can see them all week.
Direct instruction, day 1 (5 min): Explain that the town spreads salt on the road all winter, and that melting snow carries that salt off the road into the soil at the edge. Tell the class they will test whether seeds still grow when the water reaching them is salty. Name the one thing that will be different between the trays, and name three things that will be kept the same: the seed, the light, and how much water goes on each day.
Guided setup, day 1 (15 min): Line each tray with two layers of paper towel and wet the towels with plain water. Sprinkle the same spoonful of grass seed across each tray. Label one tray Plain and one tray Salty. Mix the salty water in front of the class by stirring two spoonfuls of table salt into the cup marked salty, and tell students that only an adult mixes the salty water and that no one tastes anything in this lesson. Set both trays in the same window. Have students draw both trays on the handout as day 1.
Daily check, days 2 through 4 (15 min total, 5 min each day): Each day, two students pour one quarter cup from the matching labeled cup onto each tray. The class then writes one sentence about each tray on a wall chart, such as "Plain tray, day 3: small green tips." Students copy the two sentences onto the handout. Everyone washes hands after handling the trays.
Data review, day 5 (12 min): Set the trays side by side at the front. Have students complete questions 1 through 6 on the handout, drawing both trays first and then answering. Circulate and ask two or three students to point at the evidence in the trays for what they wrote.
Formative check, day 5 (5 min): Ask the whole class: "Both trays got water every day. Did the seeds in both trays get what they needed?" Take a thumbs up or thumbs down from every student. If fewer than three quarters give a thumbs down and name the salt when asked, hold the two trays up together and re-read the day 1 setup notes before moving on.
Closure, day 5 (3 min): Return to the three guesses from day 1 and mark which ones the trays support. State plainly that plants need water and that what is dissolved in that water matters, then connect the result back to the brown strip along Rowanwood Street.
Student Handout
Day 1. Draw your two trays. Write the date under each drawing.
Days 2, 3, and 4. Copy the class sentence for each tray.
Day 5. Answer these questions.
- Both trays got the same seeds, the same light, and the same amount of water each day. Name the one thing that was different.
- Both trays sat in the same window. Tell why that matters for our test.
- Draw the Plain tray and the Salty tray as they look on day 5.
- Which tray had more green sprouts on day 5?
- The seeds in the Salty tray did get water every day. Tell what happened to them anyway.
- The grass beside Rowanwood Street turns brown every spring. Use your two trays to tell why.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: The salt in the water. Only the Salty tray was watered with salty water, and everything else about the two trays was kept the same.
- Answer: Both trays needed the same light so that light could not be the reason for a difference. Accept any answer naming a fair test or keeping the sun the same for both.
- Answer: Accept any pair of drawings that matches what the class trays actually look like on day 5. In most rooms the Plain tray shows green sprouts and the Salty tray shows few sprouts or none.
- Answer: Accept the answer that matches the class trays. In most rooms the Plain tray has more sprouts, because the salty water kept the seeds in the other tray from growing well.
- Answer: Accept any answer saying the seeds grew poorly or did not sprout even though they were watered. The point to look for is that water alone was not enough once salt was in it.
- Answer: Accept any answer connecting the road salt to the trays, such as melting snow washing salt off the road into the grass at the curb, the same way the salty water reached the seeds in the Salty tray.
Differentiation
Support
Pair these students with a partner for the daily pour and give them a handout with the day 2 through day 4 sentences already printed, leaving only a box to draw in. For question 6, offer two written choices, one naming the salt and one naming the cold, and ask them to circle the one their trays support.
Extension
Ask a small group to set up a third tray watered with water half as salty as the Salty tray, mixed by the teacher, and to predict before day 5 whether it will look more like the Plain tray or the Salty tray. Have them report what they found and whether their prediction held.
ELL supports
Label each tray with a picture as well as a word, a water drop for Plain and a salt shaker for Salty, and keep the labeled cups beside the matching trays all week. Provide the sentence frames "The ___ tray has ___ sprouts" and "The salt made the seeds ___," and allow question 4 to be answered by pointing at a tray.
Extensions
Walk the class along the edge of the school parking lot or driveway in early spring and mark with flags where the grass is brown and where it is green. Keep the class on the grass, away from moving cars. Ask students whether the pattern of flags matches the pattern in their two trays.