Mathematical thinking and reasoning are at the core of mathematics learning, strategies to facilitate their development are global issues for various countries. This qualitative study aims to describe the fifth-grade elementary school teacher’s stimulus form, to expand students’ thinking ability in mathematics learning and obtain a stimulus formulation of the fifth-grade elementary school teacher in developing students’ mathematical thinking ability. Data were obtained by using open-ended questionnaire methods and passive participation observation. The study results showed that the stimulus form of the fifth-grade elementary school teacher in expanding students’ thinking skill in learning the mathematics comprises problem posing, asking guiding questions, facilitating technology (learning videos/PowerPoint/Plickers), and song. The recommendation of fifth-grade elementary school teacher stimulus for developing students’ mathematical thinking ability was asking the probing question, playing, and games. Furthermore, the results of the second year’s research were widely disseminated to teachers. Primary school teachers who are part of the teacher working group also need to improve their professionalism, especially concerning developing stimulus thinking and applying it in learning. Therefore, the follow-up as the management of learning in the form of INNOMATTS training.