After a day of talks with a mediator, Federline's attorney Mark Vincent Kaplan told E!, "The mediation didn't result in an agreement that would avoid the trial set in August ... The mood was comfortable, positive and it was a mood that was consistent with opening at least a great dialogue, which is necessary."
Kaplan added that his client is seeking sole physical and legal custody of sons Preston, 2 1/2, and Jayden, 1 1/2, and wants Spears to continue her current visitation terms.
The singer has been spending three days a week with the boys and was recently granted overnight privileges.
"If the existing arrangement was acceptable to both parties ... we wouldn't have to go to trial," Kaplan said. "But that didn't happen."
The trial, which is scheduled to begin Aug. 25, would result in a final custody ruling, which can remain in place for years – unless one parent successfully convinces the court to modify it.
"It's very likely both Britney and Kevin will testify in a trial," says L.A. family lawyer Lynn Soodik, who's not involved with the case. "Britney has to show the court that she's improved as a mother. If she loses, the gut-wrenching part is that she could miss out on a significant portion of her kids' childhoods.
"However, since she's under conservatorship, it's unlikely she'll win any legal custody," Soodik adds. "If she can't make decisions for herself, how can she decide things like which doctors, schools and religion, if any, are best for the kids?"
Still, says Soodik, "It's possible that both sides can settle at any time."
Calls to lawyers for Federline and Spears were not returned. Their next hearing is set for July 15.