Cambridge University psychology professor Michael Lamb is one of the foremost authorities on fatherhood and child development.
He testified for the plaintiffs who want the marriage ban declared unconstitutional.
"And he made a number of points the key points included that children parented by gay men and lesbians are as likely to be well adjusted as children who are parented by heterosexual parents," plaintiff's attorney Theodore Boutrous said.
Lawyers arguing against the state ban on same-sex marriage summarized Lamb's testimony, and said a number of expert witnesses for the other side have withdrawn, but not for the reason's they stated.
"The reason they withdrew those expert witnesses was not because of cameras. It was because they did not want to subject them to cross examination by David Boies," Boutrou said.
Boies says in depositions before the trial, two of the expert witnesses for Prop 8 changed their testimony.
"And they essentially gutted the case of the defendants, and that's why they chose not to bring them," he said.
A lawyer arguing for the Prop 8 ban said he didn't know anything about that pretrial deposition, but he believed the witnesses withdrew because they didn't want their pictures broadcast.
"Their concern was the same that other have that they will be targeted for retaliation -- both professionally and personally," Attorney Andy Pugno said.
Pugno discounted Lamb's testimony, pointing out Lamb is a professor and not a clinical psychologist.
"Has never treated a patient and hasn't even interviewed a child in the last 20 years," he said.
The Prop 8 lawyers also argued child rearing isn't the core issue before the court.
"If there is a reasonable basis for the voters to make their decisions, then it's enough for the courts to uphold that. They should do that and not insert themselves into making policy and weighing scientific evidence," Pugno said.
Attorneys wrapped up the week with testimony from Helen Zia, a San Francisco lesbian who married her partner in 2008. She testified that marriage "has strengthened her family."
Court resumes Tuesday, and a major proponent of Prop 8 is expected to take the stand.