Mathematical tasks has important role in promoting students’ mathematical ability. However, most of students can not do by themselve in improving their ability. They still need supports from their teacher. This paper describes the way that teachers can do in promoting students’ reasoning ability. Some mathematical tasks using Covid-19 context were develoved and used in learning sequences. Design research type validation study was chosen as research method. The data were collected through interview, observation, and students’ worksheet, and they were analyzed qualitatively. The results showed that some supports that teachers need to do in promoting students' reasoning ability such as: asking students whether they understand the problem given; asking the reason behind students’ answers; not giving judgement of students' answers directly; asking the other students’ opinion or answers; and comparing the difference among students’ answers.