The answer is David. Did you get it correct?
How come David gets assigned to School A first before Peter even though he put it as his second choice ?
The posting exercise will actually look at all the posting requests of students based on their results, with the higher-scoring students being attended to first. So if your child has a higher score, the system will consider ALL the 6 choices of your son first, and try to post him to a school that is highest on his list but which still has vacancies.
Experiment #7 - Forces (Frictional Force)
Experiment #6 - Forces (Frictional Force)