In the Progressive Era, reformers tried to increase the power of the middle class and tried to reform American society to make more people act like members of the middle class. This is what social and political reform meant in those days.
Political reform meant taking power away from the rich and from political machines and giving it to the middle class. This included reforms such as non-partisan, at-large elections in cities and the direct election of US Senators.
The most important progressive social reform was Prohibition. This was meant as a way to stop poor people (especially immigrants) from drinking so they could become responsible people like the members of the middle class. (This is, of course, from the point of view of the reformers.)