Yesterday Straits Times had a report on PW grades huge disparity. They say HCI got 85% A, MJC got 50% A, RJC got 40% A. TJC got 7% only, SAJC got less than 1% (which insider says its 0.3%, dunno whether its true or not). I believe HCI and MJC got teachers help one, they do draft 5 or 6 times, in the end become all teacher's idea, not their idea, also the OP not very fair, most classes get their own school teachers, not external mod, not enough external mod for all classes one.
MOE needs to review PW assessment, every year sure got schools complain or get very low or very high marks.
HCI and MJC most probably cheated through their PW without letting their students know