This paper describes the Rational Number Project (RNP), teaching experiments concerned with the teaching and learning of fractions among 4th and 5th grade students. Interviews with 4th grade students who used the RNP curriculum and with students who used a traditional curriculum were conducted by RNP staff as well as classroom teachers. This paper provides teachers with examples of students' conceptual and procedural thinking to give them a picture of what it means for students to exhibit number sense with fractions. Focusing on children's thinking and the effect of the use of manipulative models on children's thinking is suggested as one way of teaching fractions. (KHR)