I have, over the years, noticed that barbs will do better in odd schools. I would keep at least 5. Like everything else in aquariums, there are exceptions. You may get that one barb that is a spawn of satan and will not behave no matter what you do. Most of the time though, the odd schools will reduce agressiveness. Barbs should still only be kept with fish that can handle their behaviour. No angels, bettas, ect...
Life is not measured by the number of breaths we take, but by the moments that take our breath away.