That's probably how your school works.
Many schools have their own systems of grades and extracurricular activities. When I was growing up, we had a 6-weeks system. A full year of school is 36 weeks. So, we have six 6-weeks. At the end of each 6-weeks, we get a report card. At the end of the 3rd week of each 6-weeks, we get a progress report. The progress report is what most coaches and supervisors look at to determine if the students can stay in the group or not.
If there was a concern (a student suddenly fails a test and a quiz after doing well), then action would likely be taken.
Most of the time, they would simply put the student on hold for a week or two (likely 3 weeks) until that student shows improvement.