This study is qualitative in nature, aims to examine the patterns of interaction that are constituted in a realistic mathematics instructions at grade 5 viewed from the use of scaffolding. As the subjects of this study were 21 fifth grade students of an elementary school in Surabaya, who learned mathematics in small groups and whole-class interactive lessons. The data were collected through four lessons taught in the same class by the same teacher. The classroom observations were videotaped, while field notes were also taken. During the teaching experiment, the students learned mathematics using realistic approach in the material of statistics. The research subjects were grouped into four or five students per group, by considering heterogeneous characteristics. The data were collected using the following instruments: (1) Observation sheet of the learning process, (2) Observation sheet for students’ activities, and (3) Handycam, to record the process of mathematics teaching and learning with realistic approach, especially the interactions which were present during the teaching experiment, and the use of scaffolding by the teacher to promote students’ understanding of the mathematics concept. The observation sheets filled out by observers by giving a score corresponds to the range given for every aspect which was observed. The observations results were then analyzed using descriptive-qualitative method, while the recorded data were analyzed qualitatively. The researcher transcribed the video recordings for comprehensive analysis, and then performed data reduction as well as data presentation. The structure and characteristics of instructional interactions were analyzed, and finally the researchers drew conclusions based on the available data and the results of data analysis. The comprehensive data analysis revealed that students engaged in productive interaction and inquiry while they were learning mathematics in small groups or in whole class setting. During the whole class setting, the most frequent interaction patterns were encouraging students to explain their solutions, and to express their thinking and opinion about the other group presentations. During the four teaching experiments, in the introduction phase, the teacher  gave scaffolding in the form of environmental provision, while in the main activity phase and the closing of the lesson, the scaffolding given by the teacher were in the form of reviewing, restructuring, and developing conceptual thinking. It means that by participating in interactive discussion and learning, the students are habitually engaged in productive interactions and high level of mathematical thinking.