This study was conducted to develop a supplementary material on the modes of heat transfer for promoting STEM learning among grade 7 students. The supplementary material went through the following stages of development: identification of the topic, draft, evaluation by the thesis adviser and panel members, revision, final evaluation by the in-service teachers and preservice teachers, test for readability, and final revision. The developed supplementary material was found suited for the Grade 7 students by the use of the McLaughlin SMOG formula for the readability. Hence, the supplementary material is highly commendable as an instructional material and it can be a tool for promoting an effective STEM learning.