Classroom activity Grade 6 Math
Prescott Impervious-Surface Percent Grid Game
A grade 6 team game where students cover a 100-square grid to model a fictional block's paved area, reading each square as one percent to compare stormwater runoff.
Objectives
- Students will read each square of a 100-square grid as one percent of a city block.
- Students will find the percent of a block that is paved and rank blocks by runoff.
Vocabulary
Key words: percent, impervious, pervious, runoff
Teacher overview
This is a team game for groups of three or four students. Each team gets a 10-by-10 grid that stands for one block in the town of Prescott, a fictional town, with each of the 100 squares equal to one percent of the block. Teams color squares to show paved surfaces, which are impervious, and open surfaces like lawns and rain gardens, which are pervious. Because each square is one percent, counting paved squares gives the percent impervious directly, and more paved area means more rain runs off to the storm drain.
Activity Directions
- Before class, print three 10-by-10 grids for each team, one per round, and set out two colors. Tell the class that gray will stand for pavement, which water runs off of, and green will stand for lawn or rain garden, which water soaks into.
- Put students in teams of three or four and give each team one grid. Explain that the grid is one block in the fictional town of Prescott, and each square is one percent of the block.
- Round 1, the shopping center (8 min): call out "color 70 squares gray for pavement, and color the rest green." Each team then counts its gray squares and writes the percent impervious, and counts its green squares for the percent pervious.
- Round 2, the neighborhood park (8 min): on a fresh grid, call out "color 20 squares gray for pavement, and color the rest green." Teams write the percent impervious and percent pervious again.
- Round 3, design your own (10 min): teams design a block that keeps the paved area at or below 40 squares, color it, and write its percent impervious. Then teams trade grids with a neighbor and check that the neighbor stayed at or below 40 percent.
- Ranking (6 min): line up the three blocks (shopping center, park, and the team design). Teams rank them from most runoff to least runoff based on the percent impervious.
- Debrief (8 min): gather the class and discuss four questions: what percent of the shopping center is impervious and pervious, what percent of the park is impervious and pervious, which block sends the most rain to the storm drain and why, and what happens to runoff when paved squares are replaced with a rain garden. The Answer Key gives the expected answers. Connect more pavement to more runoff and more strain on the storm drains.
- End the game after the debrief. Collect the grids as an exit check that each team labeled a percent on every block.
Student Handout
Fill in one row for each block as you play. Remember: each square is one percent of the block.
| Block name | Gray (paved) squares | Percent impervious |
|---|---|---|
Ranking, most runoff to least runoff: write the three block names in order from 1 to 3 below.
- Block with the most runoff:
- Middle block:
- Block with the least runoff:
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: 70 percent impervious and 30 percent pervious. In round 1 the shopping center has 70 gray squares out of 100, so 70 percent is paved and the other 30 squares are 30 percent pervious.
- Answer: 20 percent impervious and 80 percent pervious. In round 2 the park has 20 gray squares out of 100, so 20 percent is paved and 80 squares are pervious.
- Answer: The block with the most gray squares sends the most rain to the storm drain, because a higher percent impervious means more water runs off instead of soaking in. The shopping center (70 percent) always ranks highest. The park (20 percent) ranks lowest unless a team's own design has fewer than 20 gray squares, in which case the team design ranks lowest.
- Answer: Replacing paved squares with a rain garden lowers the percent impervious, so less water runs off and more soaks into the ground.
Differentiation
Support
Give teams a grid with the outer border already shaded so counting to 100 is easier, and let students count paved squares in groups of ten. Pair a strong counter with a student who needs support during the coloring rounds.
Extension
Ask teams to redesign the shopping center block to cut its percent impervious to 50 percent or less while keeping the same number of parking spaces, using rain gardens between rows, and to explain the trade-offs in one or two sentences.
ELL supports
Pre-teach "paved," "impervious," "pervious," and "runoff" with a photo of a parking lot next to a lawn. Use the two color words consistently, and label the grid key in both English and students' home languages where possible. Allow students to say answers by pointing to gray and green squares.