Lina, a Mexican American second grader, bilingual in Spanish and English, used a strategy for adding two two-digit numbers that the authors share as an example of the importance of listening to the mathematical ideas of children, especially when these ideas do not align with how mathematics is traditionally represented in the classroom. The authors interviewed Lina using guidelines for clinical interviews in which the goal of the interview is not to guide a child to the correct answer but to ensure that the interviewer understands the mathematical reasoning of the child's strategy. This example highlights that teachers can support a climate in which the details and ideas brought into the classroom by children can inform teachers' instructional decisions.