Reynoldsburg school officials were phasing out the use of Social Security numbers in the district's student database when someone stole a laptop containing that information.
The district laptop, taken from a computer technician's car on Saturday, also included names, addresses and phone numbers for 4,259 students, about two-thirds of the district's enrollment.
The computer technician had been using the laptop to transfer student information into a computerized lunch-payment system at each of the district's schools, said Assistant Superintendent Dan Hoffman.
He completed that work last week but didn't delete the information from the laptop, which was stolen from his car while he was at a wedding in Columbus.
He filed a police report Monday but didn't realize that the student information was in the laptop until Wednesday, Hoffman said.
"As a district, we're assuming the responsibility for this loss," Hoffman said, "although we think there was poor judgment used by the employee in leaving the laptop in the car."
The district used an automated system to call affected families today, and a letter from Superintendent Steve Dackin will be sent home Friday.
Columbus police, the district and its insurance company are all investigating. The technician is on paid leave.
Reynoldsburg officials are considering policies, such as requiring staff members to take more care with district property, to prevent similar events.
"We recognize that the security of state data is a systemwide responsibility," Hoffman said.
Since January, the district stopped requesting Social Security numbers from students as it creates a new database. Officials planned to switch to the system this fall.
Last year, a computer backup tape that contained banking information for more than 770,000 taxpayers, along with nearly 259,000 businesses, vendors or other entities, was stolen from a state intern's car.