@article{ref1,
title="Class and ethnic differences in the responsiveness of preschool children to cognitive demands",
journal="Monographs of the society for research in child development",
year="1968",
author="Hertzig, M. E. and Birch, H. G. and Thomas, A. and Mendez, O. A.",
volume="33",
number="1",
pages="1-69",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0037-976X",
doi="",
url="http://dx.doi.org/"
}