Improve student mathematical communication ability through the development of geometry instructional device based on Van Hiele's theory

Mathemathical communication ability is one of the mathematical abilities that need to be developed for students, so that students are able to solve mathematical problems and other sciences as well as being able to provide logical, systematic, critical and open reasoning skills needed in everyday life. The results of the literature study and preliminary study state that students' communication abilities are still low. This is because students are less active in the learning process and are not used to expressing mathematical ideas. Therefore, a learning device based on Van Hiele theory is designed which is expected to later be able to improve students' mathematical communication skills. This research is a development research by adapting the development model of Plomp consists of 3 phases, namely preliminary research, prototyping phase, and assessment phase. The research subjects were class VII students of SMPN 13 Padang. At the preliminary research phase needs analysis, curriculum analysis, analysis of the characteristics students, and concept analysis. In the prototyping phase, the design of lesson plan and students worksheet based on Van Hiele theory, then formative evaluation is carried out to determine the validity and practicality of the product. In the assessment phase an assessment is carried out with limited practicality and effectiveness. Practical data is obtained from the implementation sheetof lesson plan, teacher practical questionnaire, students practical questionnaire. Effectiveness data obtained from student learning outcomes in the formof a final test to see the mathematical communication abilities of students. The results showed that learning sets based on Van Hiele theorywere valid, practical and effective. Valid because it meets the criteria valid in terms of content and construct. Practical because it is easy to use and understand, the allocation determined is very efficient, interesting, and contributes to learning. Effective in terms of its potential impact on the communication ability of mathematical learners.