It also increases dopamine and norepinephrine activity in certain areas of the brain, similar to Adderall and Ritalin, so it will boost your concentration. It actually showed a positive effect on concentration in ADHD treatment trials, but the FDA declined to approve it for that purpose due to some concerns over a rare skin-rash disorder. Many people are under the misconception that it is not a stimulant, but it most certainly is.
As for controlled, double-blind trials, the results are not promising in non-sleep-deprived individuals. Controlled tests tend to show self-reported increases in restlessness, aggression, and anxiety, but the standardized cognitive and memory tests show very little, if any, improvement in the Modafinil groups. (See http://www.ncbi.nlm.nih.gov/pubmed/12672167 and http://www.ncbi.nlm.nih.gov/pubmed/15738750 for more).
Finally, don't try to import Modafinil (Provigil) into the US without a prescription. It is a Schedule IV controlled substance and the legal ramifications for importing a controlled substance can be serious. If you're still eager to try it outside of a doctor's supervision, which I definitely do not recommend, then know that Adrafinil is metabolized (partly) to Modafinil within the body but is not a controlled substance. Importing it is a still a gray area, though.
Bottom line: Getting a healthy amount of sleep should be your #1 goal for cognitive improvement. If that isn't actually possible, then Modafinil could be helpful for reversing the effects of sleep deprivation. If concentration is your problem, Modafinil may help you, but you'd probably be better off pursuing proper ADHD treatment with a medication approved for ADHD.