There's a
large body of evidence that chewing gum, at least in the short term, is a real benefit to the brain. In one recent study, for example, gum-chewers (with or without sugar) performed "significantly" better on five out of six tests than non-chewers. Curiously, though, it seems that the benefit only lasts for about 20 minutes, and nobody's sure why, or if there's some sort of a "refresh period" after which it would become effective again.
Regardless, it seems funny that the one simple thing that would help students learn is pretty much banned from most classrooms. Not to mention Singapore.