Z-Score (Standard Score)
9-12
A z-score tells you how many standard deviations a value is from the mean, calculated as $z = \frac{x - \mu}{\sigma}$. Positive z-scores are above the mean; negative z-scores are below. Z-scores allow comparison of values from different distributions.
"Z-scores put everything on the same scale. A z-score of +2 means 'two standard deviations above average' - unusually high. A z-score of -1 means 'one SD below average' - somewhat low but normal."
Why it matters: Z-Score (Standard Score) helps students read data as a whole pattern instead of a pile of disconnected values. That habit matters because many statistical decisions depend on where a value sits in context, how symmetric the pattern is, and whether a simple summary would hide important structure.