BrekkeB.WilliamsJ. D. (1973) Conservation and sexPerceptual and Motor Skills, 37, 14.
2.
GoldschmidM. L. (1967) Different types of conservation and nonconservation and their relation to age, sex, IQ, MA and vocabularyChild Development, 38, 1229–1246.
3.
WilliamsR. (1971) Testing for number readiness: Application of the Piagetian theory of the child's development of the concept of numberJournal of Educational Research, 64, 394–396.
