O-levels query

[alliekiwi.livejournal.com]

I was re-reading The Attic Term today and got a little confused as to the period over which Patrick took his O-levels.

For example, a page or two before the end of chapter 10 is the following passage:

~*~*~
Being anything but reckless, Ginty had meant to let at least two weeks go by before phoning Patrick again: and then, on the Monday evening, listening to the other four deciding to play ping-pong in the gym and mentally preparing a plausible Cat-That-Walked withdrawal, remembered that Patrick's O-levels began tomorrow: she ought - she must - phone and wish him luck.
~*~*~

Following that we have half-term which is when Miranda and Tim write the short Christmas carol for Nick to sing etc. Patrick has his half-term the week after Kingscote, and then along comes Chaper 13 and the fateful Maths O-level paper debacle. The chapter starts:

~*~*~
In the summer term, the sitting of O- and A-levels was something of an occasion: Miss Keith announced their commencement during Assembly and wished the candidates well on behalf of the school. But in the winter term, when a mere handful of unfortunates was at risk, the event was hardly mentioned, and it was only because Ginty was sitting-in on the Tutorial fifth's Latin revision that she knew when O-levels would make their delayed start as soon as Patrick did. Telephoning him that evening, she found him depressed and edgy.
~*~*~

Why is Patrick 'starting' his O-levels twice like that?