DETROIT -

Both sides in this trial agree on one thing: April DeBoer and Jayne Rowse are good parents to the children they are raising together.

But sociologist Mark Regnerus, who studied 3,000 young adults, concluded that children with a gay or lesbian parent do relatively poorly. On Tuesday, ACLU lawyer Leslie Cooper grilled Regnerus for comparing that group only to people who spent their entire childhood with their biological parents.

Regnerus works at the sociology department at the University of Texas, which said this week in a statement: The conclusions he draws from his study of gay parenting are fundamentally flawed.

Regnerus testified on Tuesday: "It's regrettable. The university is characterized by academic freedom. They've apparently been getting negative press."

Cooper pointed out previous studies showing challenges for children from families with low incomes or low education levels.

Cooper: It is not your view that marriage should be limited to those groups whose children are statistically most likely to have positive outcomes?

Regnerus: No.

Cooper portrayed Regnerus as a hired gun for the Witherspoon Institute, a conservative think tank which funded his study. He denied that the study was rushed to influence a Supreme Court case on gay rights and said the conclusions were his own.

Read back: Roger Weber blogs from trial over Michigan's gay marriage ban