Vasserly Creek Sampling: Comparing Two Sites by Center and Spread

Hook (5 min): Write two numbers on the board, a mean of 3.60 and a median of 2.85, and tell students both describe the same eight readings from one fictional creek site. Ask what could make those two numbers disagree by that much, and collect three or four ideas without confirming any of them.

Direct instruction (12 min): Review the three statistics the lesson uses. Model each one on a short teacher example that is not on the handout: the five fictional readings 1.5, 1.6, 1.8, 2.0, and 6.0. The mean is 12.9 divided by 5, which equals 2.58, while the median is 1.8. Show the quartile positions on that same list, then state the outlier rule: a value above the third quartile plus 1.5 times the interquartile range is treated as an outlier. Do not work any handout number during this segment.

Guided practice (12 min): Distribute the handout. Work items 1 through 4 together, pausing after item 3 so pairs can confirm they divided by 8 and not by 7. Ask students to write one sentence predicting whether the two sites will have similar spreads before they compute anything in item 7.

Independent practice (13 min): Students complete items 5 through 12 on their own or in pairs. Circulate and check that quartiles are being read from the sorted list rather than the original order, which is the most common error at this stage.

Closure and formative check (8 min): Collect the handouts and read item 12 aloud as an exit question: which measure of center better represents a typical week at the downstream site? Ask for a show of hands for mean and for median. If more than one-third of the class chooses the mean, reteach the outlier segment before the next class using the item 10 recomputation as the anchor example.