The purpose of the study was to investigate the relationship among the knowledge proposed by school curriculum, the content offered by a mathematics teacher, and what was acquired by students regarding quadrilaterals in the 5th grade, using Didactic Transposition Theory. To examine the transposing process, a case study involving a mathematics teacher and seven students was adopted in Turkey. The objectives of the curriculum were scrutinized in order to identify the content to be offered to the students. The content offered by the teacher was revealed by the records of the teaching process and the interviews with the teacher. To collect data regarding the acquired knowledge, two different tests were used. Data were analyzed utilizing document analysis, content analysis, and descriptive analysis. Findings revealed that there were significant differences between the knowledge to be taught and the content offered by the teacher. Moreover, the knowledge acquired by the students was limited to the basic properties of quadrilaterals. What was acquired by the students regarding the mathematical concept of area was not compatible with the content offered by the teacher, so the perimeter-area conflict occurred in the minds of the students at the end of the transposition process.