The importance of equal sign understanding in the middle gradesKnuth, E. J., Alibali, M. W., Hattikudur, S., McNeil, N. M., & Stephens, A. C. (2008). The importance of equal sign understanding in the middle grades. Mathematics Teaching in the Middle School, 13(9), 514-519. https://doi.org/10.5951/MTMS.13.9.0514