Measures
SES and language use at home
To obtain background information on children’s home environment, at Wave 2 (when the children
were age 5 years) oral interviews with the mothers were conducted by a research assistant who was a
native speaker of Turkish. SES background was measured through parental level of education and was
calculated as the mean of the highest attained educational level of both parents rated on a 6-point
scale. Parental education is the most commonly used index of SES background, is highly predictive
of other SES indicators (e.g., income, occupation), and is a better predictor of cognitive performance
than other SES indicators (for further discussion, see Calvo & Bialystok, 2014). Among the mothers
of the bilingual children, 33 reported speaking only Turkish at home, whereas 27 reported using both
Dutch and Turkish at home. In addition, 4 mothers spoke only Dutch at home but reported that their
partners spoke Turkish. For the remaining children, it was not specified how much Turkish and Dutch
was used at home.