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Measurements at the beginning of the 4th grade (when the national average is 4.0) and of the 6th grade in 25 schools in New Haven.
data(achieve)
A data frame with 25 observations on the following 4 variables.
4th grade reading
4th grade arithmetic
6th grade reading
6th grade arithmetic
John A. Hartigan: Clustering Algorithms. Wiley, New York, 1975.