Key points are not available for this paper at this time.
Kellogg W. Hunt, Syntactic Maturity in Schoolchildren and Adults, Monographs of the Society for Research in Child Development, Vol. 35, No. 1, Syntactic Maturity in Schoolchildren and Adults (Feb., 1970), pp. iii-iv+1-67
Kellogg W. Hunt (Sun,) studied this question.