The answer to this depends to some extent on who you ask and on how you define effective.
In one sense, the policies with respect to poverty in the US have not worked. If we say that poverty policy started with President Johnson's War on Poverty in the late 1960s, we can see that the percent of Americans living in poverty has actually gone up since Johnson's time.
However, there is some controversy over the meaning of this sort of statistic. Conservatives would say that this proves that liberal antipoverty programs do not work. But liberals would tend to say that antipoverty programs have worked but that they have not reduced poverty because the country has never really committed to them or has not carried them far enough. From this point of view, the programs would work if only politicians would vote to fund them fully and extend their impact.
Overall, then, it seems clear that antipoverty programs since Johnson's time have not had an effect on reduced poverty. The real conflict is over why this is so.