The aim of this action research is to develop the skills of elementary teacher candidates in designing 21st-century learning activities. Action research, one of the qualitative research methods was applied in the study. Some criteria were determined and the applicability of the criteria were tested by the participants. Data were collected from two groups in two different education terms. The criteria sampling method was used for determining participants. The first group has 52, while the second group has 42 elementary education teacher candidates (ETCs). A rubric to design learning activities was created with ETCs in the first term and they applied them as a performance homework. In the second term, ETCs experienced by applying revised rubric to design 21st-century learning activities. They also fulfilled a self-assessment form to tell their experiences. Collected data were analyzed document analysis, descriptive analysis, and content analysis methods. Findings indicated that ETCs have developed professional and personal skills by designing 21st-century learning activities.