Children that grouped the piece of yellow rope with the yellow stick were noted as classifying objects on the basis of colour, while children that grouped the piece of yellow rope with the piece of blue rope were noted as classifying objects on the basis of shape/form.
As predicted, Navaho-speaking children tended more strongly to classify objects on the basis of shape/form than English-speaking children. In both groups, classification based on shape/form increased with age, but later and less marked in children speaking English than in children speaking Navaho. These results seem to confirm the linguistic relativity hypothesis.
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.