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This report describes the longitudinal changes that took place in the average fundamental frequencies (fo) of 25 boys and girls over a 3-year period (means age range = 8:2-11:2). Results showed that developmental changes in the central tendency of fo can be detected over a 1-year period. For the group, the amount of decrease per 12-month interval averaged about 12 Hz, with a standard deviation of about 8 Hz. Cross-sectional observations of 7-11-year-old children's fundamental frequency characteristics do not reflect accurately the developmental course of fo, in large part because the between-subject standard deviations are larger than the age-related changes that occur in children's voices at this stage of development.
Suzanne Bennett (1983) studied this question.