title: Equivalence formation by retarded and nonretarded children structured and unstructured tasks.
mesh_terms: D000704:Analysis of Variance; D002648:Child; D003210:Concept Formation; D004495:Education of Persons with Intellectual Disabilities; D005260:Female; D005556:Form Perception; D006801:Humans; D007804:Language Development; D008297:Male; D012718:Set, Psychology; D013561:Symbolism