Putting the "th" in Tenths: The Role of Labeling Decimals in Revealing Place Value Structure

Language is a powerful cognitive tool. For example, labeling objects or features of problems can support categorization and relational thinking. Less is known about their role in making inferences about the structure of mathematics problems. We test the impact of labeling decimals such as 0.25 using formal place value labels (“two tenths and five hundredths”) compared to informal labels (“point two five”) or no labels on children’s problem-solving performance. Thirdand fourthgraders (N = 104) were randomly assigned to one of three conditions (formal labels, informal labels, or no labels) and labeled decimals while playing a magnitude comparison game and number line estimation task. Formal labels facilitated performance on comparison problems that required understanding the role of zero, which highlighted place value structure. However, formal labels hindered performance when explicit understanding of place value magnitudes was required. Findings highlight how the language teachers and students use can impact problem-solving success.