Four weeks seems ludicrously short too. I'm curious about this because my sister is ludicrously good at languages (learned to speak ridiculously early, became fluent in Hungarian in less than six months etc.) but I'm not sure you'd necessarily distinguish between me and her after just four weeks of classes in most languages. Also Mandarin is a tonal language so could be totally different cognitively from non-tonal languages. It depends too on what you are testing - I know after my first month learning Mandarin, I'd have got full marks on a test with pinyin but done terribly on any sort of aural test. Very different skills.

So, by brains wired for languages they actually meant "wired" for teaching methodologies at schools that are known not to be effective for teaching languages to begin with.

The first thing I thought was: so they're good at taking tests? How is this related to actual langue.

Came to the comment section to say the same thing. I think it would have been more worthwhile for us to read the study directly, and draw our own conclusions.

As a beginning Mandarin student myself, four weeks of classes means absolutely nothing about fluency in the language (assuming the students are native English speakers). It's a very difficult language to learn, and four weeks doesn't have you engaging in unscripted conversations with fellow students. The low n is understandable, but only four weeks of classes is pointless.