When, however, the same experiment was performed on English-speaking
white middle-class children in Boston, their performance was more similar to the
Navaho-speaking children than to the English-speaking children from the reservation.
Their preference for shape/form-based classification was slightly weaker in the
earliest age group, but later was actually stronger than that of the Navaho-speaking
children. The proposed explanation is that other non-linguistic factors associated with
social class overrule the effect of language. This explanation seems to be confirmed
by a later experiment with English-speaking schoolchildren in lower-class Harlem,
whose performance was very close to the English-speaking children in the Navaho
reservation