Last week, school officials in Des Moines were celebrating improved marks on a state evaluation. The superintendent, Ian Roberts, who in two years on the job had already become a well-known figure in Iowa, said the report showed “that we have the foundation of an outstanding school district that will continue to grow and improve.”

Days later, the Des Moines Public Schools system was in disarray.

Dr. Roberts was in the custody of federal immigration officials, who asserted that he had been leading the school system while in the United States illegally. District officials were struggling to answer questions about their vetting process for hiring Dr. Roberts and straining to square the description of Dr. Roberts by Immigration and Customs Enforcement officials with the man they knew. On Saturday, School Board members voted 7 to 0 to place Dr. Roberts on paid administrative leave during a meeting that lasted less than three minutes.

“I want to be clear, no one here was aware of any citizenship or immigration issues that Dr. Roberts may have been facing,” said Jackie Norris, the School Board chair, in a statement that she said she was reading on behalf of the Board. “The accusations ICE has made against Dr. Roberts are very serious, and we are taking them very seriously.”

Ms. Norris, who is running for a seat in the U.S. Senate as a Democrat, said Dr. Roberts had said he was a U.S. citizen on an Iowa application for a superintendent license. Board members declined to take questions from reporters.