Ah – this is a controversial question. Some people might tell you that omega-3 fatty acids from fish oil will make you smarter – or at least able to concentrate better in class. But there is no good evidence for that – so don’t bother wasting your money on such things.
Apart from the general advice of eating a healthy and balanced diet, I am not aware of any specifc food that will help – apart from one thing.
I believe that it is important for women to have folic acid in their diet when they are pregnant. This is to ensure that the brain of the growing foetus forms properly.
However they need to have been eating folic acid as soon as the pregnancy starts. For this reason, folic acid is included in bread which most people eat every day (though it is also found in other foods).
Again as a non-expert, my impression from reading the odd pop science article is that there are several different levels of answer to this…firstly the brain is a great devourer of energy, so needs energy food – no energy, no thinking…I know if i don’t get enough to eat, my thinking can go a little awry, secondly there are a lot of superfoods that have been discredited or not scientifically proven such as taking extra fish oils (google the excellent Ben Goldacre for his views) and finally there are lots of new ‘designer’ drugs that claim to make you sharper or more insightful. Hmm. not sure about that!
I don’t think there are specific foods that do this, but a balanced diet including all the key nutrients the brain needs is important for good brain function, along with exercise (because blood pressure, and heart and lung health are important for the brain). For the same reason you should not smoke if you want a healthy brain.
There were some stories about particular fats/oils found in fish (Omega 3) being important, but these are quite controversial and the media reporting around this topic has been rather distorted (perhaps because food manufacturers would love to say “our fish fingers make you smarter”). It will probably turn out that there are aspects of our diet we can optimize for better brain health, and omega-3s may play a part in this, but be wary of extravagant health claims from food manufacturers.