They are also indebted to Dr. Gerald A. Yoakam, Director of Teacher Training in the State Normal School at Kearney, Nebraska, for the use of some of his data, and to Miss Kate Kelly, Primary Supervisor of the Des Moines Public Schools, for reading the manuscript and ofiering constructive criticisms. To many heads of school systems in Iowa who permitted the carrying out of experiments the authors are grate ful, and especially so to Misses Post, Swemm, and Starr, principals of schools in Cedar Rapids, Iowa.

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