Actually I got into OCS without either an A Level or Diploma. I
studied overseas so when I first got into BMT and they segregated
all those with differernt academic backgrounds, I was grouped into
the P6-8 and below bunch (with all my good hokkien bing friends).
They didn't recognize what a high school diploma was so they
grouped me into the lowest classification. I nearly got away with
it, but my OC forced me to go down for the Sit-Test.
So long story short, if your OC recommends you, can go in one. I
know one other chap who was homeschooled and he got into OCS. So I
don't think there's a hard and fast rule that one you have to have
an A-Level/Diploma minimum to get in. Otherwise we certainly
wouldn't.
