In general giving people a stable, appropriate calorie diet is the best way to increase IQ over a population. Poverty has a whole lot to do with that.
Next, after you lift people out of poverty you still have the education problem. Uneducated parents don't have educated kids, statistically speaking. The first few years of life, before kids are ever sent to school define a person's learning capacity hugely. Babies that have working parents and have less personal care, less emotional closeness, and less exposure to a wide range of language are going to be disadvantaged to those kids that do.