We do this in chapter 2; by chapter 8 students have forgotten

Every time I teach statistics, at least one student will ask me a question about chapter 8, whose answer is in chapter 2.

In chapter 2 we calculate the standard deviation of a sample. I invite the class to do one calculation of a sample of three numbers using each step of the formula: √ ∑(x_i - ̅x)² / (n-1). Then I show them how to do it with a single Excel function, =STDEV. At the end of chapter 2, every student can do this in Excel.

We discuss standard deviations in the subsequent chapters, such as when we do Normal distributions, but we don’t calculate any.

In chapter 8 we do hypothesis testing of two samples that are matched pairs, such as a husband’s data and a wife’s data. We take the difference between the two values in each pair, calculate the mean of the differences, and the standard deviation of the differences. And at least one student will ask how to do these standard deviations. The answer is: the same way we did them in chapter 2.

Even if you don't teach statistics, I bet you have a similar experience. Comments?