Complex sentence: Schools who implemented the EMI policy by 2000-2001 were allowed to switch to English as the medium of instruction, as was the case for certain subjects in part of the secondary 4 and 5 classes.
Split into simpler sentences: Schools who implemented the EMI policy by 2000/2001 were allowed to switch to English as the medium of instruction. This was for certain subjects in part of the secondary 4 and 5 classes.