In response to requests from Congress, the Congressional Research Service issues publications that include background studies, pro/con arguments, policy/legislative analysis and legislative histories on subjects of interest to Congress. There are several ways to get CRS reports. You can simply Google: "your topic" crs. For example, "head start" crs. You can also search the sites listed below.
For a listing of Think Tanks, see the Policy Analysis-Think Tanks tab on this guide. Hint:some to consider-National Center for Children in Poverty, MDRC, Guttmacher Institute, Urban Institute, Center on Budget and Policy Priorities, depending policy/program you choose. Others may be relevant as well.
For a list of databases to search for scholarly articles, see the journal articles box on The Social Problem-History and Policy Response tab on this guide.