Educational Psychology Vol. 30, No. 2, March 2010, 107–124 ISSN 0144-3410 print/ISSN 1469-5820 online © 2010 Taylor & Francis DOI: 10.1080/01443410903473597 http://www.informaworld.com The role of number words in preschoolers’ addition concepts and problem-solving procedures Pooja Patel* and Katherine Helen Canobi Department of Psychology, School of Behavioural Science, The University of Melbourne, Melbourne, Australia Taylor and Francis CEDP_A_447734.sgm (Received 18 May 2009; final version received 9 November 2009) 10.1080/01443410903473597 Educational Psychology 0144-3410 (print)/1469-5820 (online) Original Article 2009 Taylor & Francis 00 0000002009 Ms. PoojaPatel p_patel04@hotmail.com Preschoolers’ conceptual understanding and procedural skills were examined so as to explore the role of number-words and concept–procedure interactions in their additional knowledge. Eighteen three- to four-year-olds and 24 four- to five-year- olds judged commutativity and associativity principles and solved two-term problems involving number words and unknown numbers. The older preschoolers outperformed younger preschoolers in judging concepts involving unknown numbers and children made more accurate commutativity than associativity judgements. Children with conceptual profiles indicating a strong understanding of concepts applied to unknown numbers were more accurate at solving number- word problems than those with a poor conceptual understanding. The findings suggest that an important mathematical development during the preschool years may be learning to appreciate addition concepts as general principles that apply when exact numbers are unknown. Keywords: preschoolers; addition; number words; part–whole concepts The preschool years are an important period of learning and development in children’s arithmetic (Gelman & Gallistel, 1978; Resnick, 1992). Preschoolers are capable of appreciating various addition concepts (Canobi, Reeve, & Pattison, 2002; Gelman & Gallistel, 1978) and solving simple addition problems (Levine, Jordan, & Huttenlocher, 1992). However, a better understanding of preschoolers’ mathematical competencies and the contexts in which they can demonstrate these competencies would help educa- tors to build on children’s existing knowledge of arithmetic after they enter school. Therefore, in the present research, we investigated three important aspects of children’s early arithmetic knowledge. Firstly, we explored preschoolers’ conceptual understand- ing of key addition principles. Secondly, we examined relations between children’s conceptual understanding and their procedural skills in solving addition problems. Finally, we investigated the role of number words in children’s conceptual and procedural knowledge. Specifically, in keeping with previous findings among older children (Canobi, Reeve, & Pattison, 1998, 2002, 2003; Close & Murtagh, 1986; Langford, 1981), we hypothesised that preschoolers would make more accurate commutativity than asso- ciativity judgements, performing above chance for commutativity but not associativ- ity. Our second hypothesis was that older preschoolers would outperform younger *Corresponding author. Email: p_patel04@hotmail.com