@article{Zhang2021,
author = {Zhang, Y. and Dang, Y. and He, Y. and Ma, X. and Wang, L.},
title= {Is private supplementary tutoring effective? A longitudinally detailed analysis of private tutoring quality in China},
year = {2021},
doi = {10.1007/s12564-021-09671-3},
volume = {22},
number = {2},
pages = {239--259},
}