Hopkins (1971) investigated the stability and change in verbal, nonverbal and total IQ scores of group tests applied to students of the 1st, 2nd, 4th, 7th, 9th and 11th years. The results showed that verbal IQs are more stable than non-verbal ones, especially before high school.
QIs from group tests were shown to be less stable than Stanford-Binet IQs before the 7th year, after which the difference in stability decreases. There were considerable changes in verbal IQ scores up to grade 4 and nonverbal IQ scores in elementary school, with few changes after that.
Differences between verbal and non-verbal IQs showed little stability before the 7th grade and considerable stability after this period. The average of previous scores did not improve the prediction of future intellectual performance. Factor analysis confirmed that the variance of verbal IQ stabilizes around the 4th year and that of nonverbal IQ around the 7th year.
Reference: Hopkins, K. D. (1971). The stability and change of language and non-language IQ scores. Final report. Project No. 0-H-024. Grant No. OEG-8-70-0007(509). University of Colorado, Boulder, Colorado.
