Unlike officials at St. Xavier, administrators at Malcolm X College, a public school west of downtown, and Michigan's Oakland University decided to resume classes Tuesday.
Malcolm X evacuated students and canceled daytime classes Monday after a similar threat was found in a campus bathroom. Administrators closed Oakland because of threatening graffiti mentioning April 14.
"We feel it is safe to return to normal operations Tuesday," Oakland University Chief of Police Sam Lucido said in a statement.
The closures -- just two days before the anniversary of the Virginia Tech killings and exactly two months after the deadly rampage at Northern Illinois University -- illustrate a major challenge facing school administrators, who have to decide just how seriously to take such threats.
"It's just part of the deal these days," Oakland spokesman Ted Montgomery said.
St. Xavier and Malcolm X are located about 15 miles apart, and although the wordings in the threats were similar, there was no indication they were related, Chicago police spokeswoman Monique Bond said.
The graffiti at St. Xavier -- the second of two threats found since April 5 -- was widely publicized over the weekend, and also mentioned in updates the college posted on its Web site.
While St. Xavier administrators decided Friday to close its campuses until further notice, classes at Malcolm X resumed late Monday afternoon. Bond said bomb-sniffing dogs from the Chicago Police Department swept through Malcolm X, but campus police made the final decision about when to reopen.
Oakland, a state university in Rochester, Mich., about 20 miles north of Detroit, was to resume classes Tuesday.
The graffiti that led to its shutdown also made a reference to "4/14" but didn't specify a type or time of an attack, Montgomery said.
In the Chicago area, two elementary schools and two high schools near St. Xavier canceled classes Monday after a Saturday meeting between school officials and city police.
The fact that the threat mentioned a certain date helped administrators at Evergreen Park Southwest Elementary decide to shut down, district superintendent Craig Fiegel said. Other schools in the district -- located in the village of Evergreen Park, next to Chicago -- canceled outdoor recess and PE classes Monday.
Fiegel called violent graffiti "the new bomb threat," recalling a period in the 1960s when bomb threats were regularly used to close down institutions. He said he worries that the closures could encourage other people who get a kick out of causing chaos.
"At what point is it serious and at what point do you have to go on with it?" Fiegel said.
At Malcolm X on Monday afternoon, student Edelena Lee had not heard of the threat or that the school had been locked down.
Despite disappointment that she may have wasted a trip to campus, she had no problem with the decision to close the school, particularly so soon after a gunman opened fire and killed five students and himself at NIU, about 65 miles west of Chicago.
"I think people have issues nowadays," said Lee, 30. "You can never be too cautious."
------ Associated Press writers David N. Goodman and Jim Irwin in Detroit and Don Babwin in Chicago contributed to this report.