Before the introduction of GCSEs, students took CSE (Certificate of Secondary Education) or the more academically challenging O-Level (General Certificate of Education (GCE) Ordinary Level) exams, or a combination of the two, in various subjects. The CSE broadly covered GCSE grades C-G or 4–1, and the O-Level covered grades A*-C or 9–4, but the two were independent qualifications, with different grading systems. The separate qualifications were criticised for disadvantaging the bottom 42% of O-Level entrants who failed to receive a qualification, and the highest-achieving CSE entrants who had no opportunity to demonstrate higher ability.