Fathers often talk the talk about sharing parenting duties with mothers when it comes to a newborn. But a new study finds that couples who profess to believe in equally-shared parenting rarely do so in practice.

The researchers surveyed 181 married, heterosexual, tenure track professors with children under age two. All of the professors had access to paid parental leave. Each survey participant was asked how their handling of about 25 child-care tasks compared with their spouse's handling of the same tasks. Among the tasks:...