## Contents

**Diffusion in the Use of Teacher-designed Mathematics Instructions Materials in Singapore Schools: A School-level and Domain-specific Analysis**by*LEONG Yew Hoong, CHOY Ban Heng and CHIN Sze Looi*(pp. 1-22)**“It’s Not Just the Language”: Grade 4 Pupils’ Understanding of Fractions**by*Jenny Lou A. BERMEJO and Catherine P. VISTRO-YU*(pp. 23-54)**Least Square Estimation and Orthogonality**by*YAP Von Bing*(pp. 55-65)**How Formal should Calculus in the School Mathematics Curriculum be: Reflections Arising from an Error in a Calculus Examination Question**by*TOH Tin Lam, TOH Pee Choon, TAY Eng Guan, TEO Kok Ming and Henry LEE*(pp. 66-77)**Remembering Professor Jeremy Kilpatrick – A Tribute**by*Vilma MESA*(pp. 78-81)