Presents final findings from a large-scale, random assignment evaluation of Building Strong Families (BSF), a program offering relationship skills education to low-income, unmarried parents who are expecting or recently had a baby. The study found that BSF did not succeed in its central objectives of improving couples' relationships, increasing coparenting quality, or enhancing father involvement. In fact, the program had modest negative effects on some of these outcomes. Although attendance at group sessions was relatively low, there is little evidence of program effects even among couples who attended sessions regularly.