Good questioning skills among teachers is a basic competence to develop students' thinking skills. Much of the past research have highlighted the lack of good questioning skills in teachers, which is limited to elementary questions like initiating a lesson, which would not invite any open answers nor stimulate students’ thought processes. This study aimed to emphasize upon the role of a teacher's or mentor's questioning skills in the development of students’ critical thinking skills in Rumah Anak Sholeh (RAS) institute. By using a mixed method research design, the study took shape of a case study. With the researcher, being the key instrument, the data collection process was carried out through in-depth interviews, participatory observation, and documentation research. To ensure the validity of the data, a triangulation process was carried out. The results found that children's critical thinking skills are formed by two principles: first, teacher's questioning skills which acted as mentoring principles; second, questions framed in open-ended question model. These two principles essentially supported the function of teacher's questioning skills so that students not only received information but managed information, resulting in the development of children's critical thinking skills. The findings have interesting implications because the characteristics found in children because of the questioning model are not usually found in formal school levels. Further research is needed to measure the effectiveness of the results found in this study.