Stephanie Ann Broten, 38, and her husband, 34-year-old Darnell Alan Landrum, were each charged in Anoka County Wednesday with one count of malicious punishment.
Landrum is the girl's step-father.
Police arrived Monday evening to find a crowd of 30-50 people watching the girl as she ran in nothing but a diaper and a tank top.
Officers believe the girl had been outside for about a half-hour before a neighbor alerted police.
Police say the girl was "crying and hysterical."
The couple told police they were punishing the girl for not bringing home good grades and for failing to do her homework.
Broten told police she did not see what the problem was.
The criminal complaint states Broten told police she was simply disciplining her child by embarrassing her.
Landrum told police the 12-year-old was warned several times that if she did not start listening in school and getting better grades, she would be forced to wear a diaper and have her head shaved.
The couple appeared in Anoka County District Court Wednesday.
Bail was set for Landrum at $6,000 without conditions, or $2,000 with the condition that Landrum have no contact with the child.
Broten was released from custody and ordered to have no contact with the child.