There’s interesting research published today in Nature that suggests that our intelligence isn’t completely determined early in life, but can keep on changing throughout our teenage years. (See the BBC News article for a summary.) Of course it’s naive to think that IQ scores capture everything we’d like to describe as “intelligence”, but combining them with neuroimaging as these researchers have done does suggest that genuine changes to the brain are still happening at this stage of life. What we don’t yet know is exactly what causes IQ to rise or fall over this period — although it’s a reasonable guess that exercising the brain by thinking isn’t likely to harm it much.
For my part, I’ve been sceptical about systems that label people “bright” or “thick” at an early age ever since meeting somebody who’d got a First in maths having failed his eleven-plus exam ten years previously. I was going to point out a more general moral but I think it should already be clear what I was going to say.