We included threety pesofwords:Target,Exposure,andControl(see Table 1 for fullsetofwords).
Target word sweretaught throughexplicitdefinitions,model usage in sentences, and illustrative
gestures. Thesewordswereusedbothinthebookreadingsessionsandintheplaysessions.Exposure
words wereincludedinthebooksandplaysessionsbutwereneverexplicitlytaught.Thesewords
were includedtoassesschildren’sabilitiestolearnwordsincidentally.Finally,Controlwordswere
never presentineitherthebookreadingorplaysessionsbutwereincludedinthepre-andpost-tests
to investigategeneralvocabularygrowthoverthecourseofthetwo-weekintervention.
Each bookcontained10wordsthatwerethetargetoftheintervention(Targetwords).Hence,each
child wastaught20newwordsoverthecourseoftheintervention(2bookswith10Targetwordseach).
Each bookalsocontained4or5Exposurewordsforatotalof8(Realistic)or9(Fantastical)Exposure
words pertheme.EightControlwordsperthemewereincludedinthepre-andpost-vocabularytests.
These wordswerechosenfromlistsin Biemiller (2009) to controlforhowwelltheyaretypically
knownbyfour-year-olds.Theywerechosentoreflectavarietyofformclasses(nouns,verbs,adjectives,
and prepositions),beabovepreschoolers’knowledgelevel,and(fortheTargetandExposurewords)fit
naturally intothetextofourchosenbooks.Apartfromtheseconstraints,wordswerechosenrandomly
from thelistsandwererandomlyassignedtooneofthethreewordtypes.Althoughallofthewords
for allthreetypeswerematchedfordifficultyaccordingtostandardsdescribedin Biemiller (2009),