Montana Math MT.CORE.DATA.INT.3

MathGrades 9–12Visualizing, Summarizing, and Interpreting Data

The Standard

Understand that standard deviation measures the variability of a data distribution, and calculate standard deviation using technology.

2026 Montana Mathematics Content Standards · Data Reasoning and Probability

Teacher's field guide

What Students Need to Do: Students describe how spread out data values are from the mean. They use a calculator or spreadsheet to find standard deviation and compare two data sets.
What Mastery Looks Like: Students enter data correctly and read the standard deviation given by the tool. They can explain why a larger standard deviation means more spread when the data use the same units.
Common Misconceptions: Students may think a higher mean always means greater spread. They may confuse standard deviation with the range or use a sample calculation when the data list is the whole group.
How to Assess It: Enter 4, 5, 6 and 1, 5, 9 in two spreadsheet columns. Use STDEV.P on each column, then name the more variable set and explain your choice.

Lesson moves

Place sticky notes at 4, 5, 6 and 1, 5, 9 on two floor number lines, then compare spread before checking STDEV.P.
Ask: Two classes average 70 on a quiz, but their standard deviations are 3 and 15. Which class has more consistent scores?
Show pairs three five-number lists, have them rank the lists by spread, then check their rankings with STDEV.P.
Record five days of bus arrival delays for two routes, calculate each standard deviation, and choose the more reliable route.

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