It depends on the school's policy. Some schools do offer summer school programs for students to retake courses they have previously failed or to improve their grades in a subject. In such cases, students may be able to repeat a course in summer school to catch up or achieve better academic standing. However, the availability and policies regarding repeating courses in summer school may vary from school to school.
Therefore, it is advisable to check with the specific school or institution to determine whether repeating a course in summer school is an option and what their specific policies are.