"CAIE" stands for Cambridge Assessment International Education, which provides internationally recognized qualifications for students aged 5 to 19. It doesn't correspond to a single grade level but rather a range of stages, roughly equivalent to certain school grade levels depending on the country.
Cambridge Advanced (AS & A Level)
Pre-university qualification
Age Range: 16–19
Rough Equivalent (U.S.): Grades 11–12 (or college prep)
Cambridge Upper Secondary (O Level, IGCSE)
O Level, International GCSE (exam-based)
Age Range: 14–16
Rough Equivalent (U.S.): Grades 9–10
Cambridge Lower Secondary
Pre-IGCSE phase
Age Range: 11–14
Rough Equivalent (U.S.): Grades 6–8
Cambridge Primary
Early education focus (English, Math, Science)
Age Range: 5–11
Rough Equivalent (U.S.): Grades 1–5