Measures of central tendency--mean, median, and mode--are often used as descriptive statistics when students conduct experiments in which they take repeated measures of the dependent variable or when class data are pooled for analysis. These measures of central tendency are often used in reporting results and drawing conclusions from experiments. But all scientists know that an important feature of data is variability. These numerical representation activities allow middle school students to use mathematics and graphing skills to analyze and interpret data with this concept in mind.