This paper reports on a teaching experiment involving decimal instruction conducted with a class of elementary students (n=20) in a public school of a small city. After doing extensive work with multiplication, division, ratio, and fractions through an innovative mathematics curriculum, fifth grade students were introduced to decimal numbers. To develop their understanding of decimal notation, students worked through three open-ended, contextual problems that encouraged them to make connections between decimals and previously encountered mathematical constructs such as ratio and fraction. After instruction, students' performance on decimal tasks indicated that students developed a robust understanding of decimal concepts. Based on these positive results, the authors assert that building decimal instruction upon students' ratio reasoning and fraction sense is a key component to helping students develop meaningful strategies for understanding and working with decimal numbers. Contains nine references. (Author/MKR)