School achievement and test results for twins and singletons in relation to social background.
D000124:Achievement; D003071:Cognition; D005260:Female; D006801:Humans; D007360:Intelligence; D007802:Language; D008297:Male; D008433:Mathematics; D011247:Pregnancy; D012737:Sex Factors; D012923:Social Class; D012931:Social Environment; D013334:Students; D013548:Sweden; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014705:Verbal Behavior