Lesh, R., Post, T., & Behr, M. (1988). Proportional Reasoning. In J. Hiebert & M. Behr (Eds.) Number Concepts and Operations in the Middle Grades (pp. 93-118). Reston, VA: Lawrence Erlbaum & National Council of Teachers of Mathematics.
The SABES Mathematics and Adult Numeracy Curriculum & Instruction PD Center is managed by the staff of the Adult Numeracy Center at TERC, located in Cambridge, MA and funded by the Adult and Community Learning Services division of the Massachusetts Department of Elementary and Secondary Education.