There are hardly any school days in February and March. Maybe that's because there are a lot of students preparing for entrance exams.
「2月と3月は登校日がほぼないの。多分受験する人が多いから」はこのようにいいます:
There are hardly any school days in February and March. Maybe that's because there are a lot of students preparing for entrance exams.
hardly = ほとんど~ない・滅多に~ない
school day = 登校日
students preparing for entrance exam = 受験生
また、文の最初のほうにIn Japan(日本では)を付けるといいと思います。