How do Cambridge look at ISA marks, i.e the practical of your science a levels? Your mark in these exams depends entirely on how nice your teacher is, I know plenty of people that got 60/60 ums because their teacher basically gave them their answer, whereas I'm looking at 48/60 (45/50 raw marks, ridiculous boundaries due to the aforementioned reason of cheating.)
The reason this affects me is because if i got 95/100 in chem1, 140/140 in chem2 and 48/60 in the ISA then my chemistry AS = 94% but if they disregard my ISA then I have a 98% in chemistry (these are purely hypothetical numbers, just used for arguments sake)