The research, which also speaks to the issue of gay adoption, is summarized in the lead article of the new Journal of Marriage and Family. Scholars, at USC and New York University, looked at a range of existing studies, including research on gay and lesbian parents, finding that it's ideal if a child is raised by two parents who are "responsible, committed, stable," but that the gender doesn't cause radical differences.
Sociologist Timothy Biblarz of the USC College of Letters, Arts and Sciences says in a release about the study:
Significant policy decisions have been swayed by the misconception across party lines that children need both a mother and a father. Yet, there is almost no social science research to support this claim. One problem is that proponents of this view routinely ignore research on same-gender parents. The bottom line is that the science shows that children raised by two same-gender parents do as well on average as children raised by two different-gender parents. This is obviously inconsistent with the widespread claim that children must be raised by a mother and a father to do well.
Full scientific article available via Journal of Marriage And Family