This booklet describes and discusses a method for determining the readability level of prose passages in reading materials for children. The method discussed in the booklet assigns a value to each noun in selected passages on the basis of its frequency level on standard word-frequency charts, correlated in a number of studies with independent estimates of the difficulty of reading passages. Comparisons are made with other readability estimates, and strengths and weaknesses of the noun-frequency method are discussed in the booklet. An appendix lists 2,050 nouns graded by frequency of use in free writing of New Zealand primary school children. (MG)