Algebraic thinking, grades K-12 : readings from NCTM's school-based journals and other publications - Moses, Barbara; Usiskin, Zalman; Christmas, Paul T.; Fey, James T.; Thorpe, John A.; Steen, Lynn Arthur; Lodholz, Richard D.; Kieran, Carolyn; Chalouh, Louise; Pegg, John; Redden, Edward; Heid, M. Kathleen; et al. (National Council of Teachers of Mathematics, 1999)