Purwatiningsih, N. L. D., and I. G. A. A. Wulandari. “Portfolio Assessment Based Numbered Head Together Toward Students’ Knowledge Competency of Mathematics”. Jurnal Ilmiah Sekolah Dasar, vol. 4, no. 3, Sept. 2020, pp. 397-06, doi:10.23887/jisd.v4i3.25396.