A great number of studies on “Matter and Heat†unit have reported that many students have conceptual errors. Studies have shown the necessity of designing and using effective teaching methods in solving such problems. ASSURE teaching design model, which aims to increase the efficiency of material choice and use with systematic prior planning of teaching, was used in creating the materials which were prepared based on web-assisted modeling. In designing blended learning environment, web-assisted activities were used which included mental models as well as analogical and simulation models based on the outcomes of the 6th grade “Matter and Heat†unit. The purpose of this study is to design blended learning environments which are designed based on web-assisted modeling for “Matter and Heat†unit. Keywords: Science education, web supported teaching, matter and heat, achievement.