It's an incident sure to fuel calls for a change in how students are evaluated, reports CBS News Correspondent Jacqueline Adams.
Bruce Hagevik of CBS Station WCCO-AM reports a total of 7,989 students were affected by the mistakes on tests they took in February and April this year. Among them were as many as 336 high school seniors who were not allowed to graduate because of the errors.
The Minnesota Department of Children, Families and Learning discovered mistakes in the scoring of six questions earlier this week. The mistakes affected 47,097 tests, all scored by the National Computer Systems.
The Basic Standards Test measures skills the students should have learned by eighth grade and are designed to ensure all high school graduates have a minimum competency. Most students pass the test on their first try.
"I am outraged by the errors committed by NCS and the harm they have caused Minnesota students, families and schools," Education Commissioner Christine Jax said.
She said correct score information and an apology from the company would be mailed to all students by Aug. 21.
National Computer Systems President David Smith said the errors resulted when the test was formatted. The order of some questions was changed, and the answer key to one test version was corrected to match, but not the other, he said.
"We make no excuses. This is completely unacceptable to our company, as it is to everyone in Minnesota," Smith said. He said the company will offer $1,000 in tuition aid to students who failed to graduate due to the errors.
The workers who made the error have been fired.
The truth was revealed thanks to one persistent father, Marty Sweden, who says, "It's astounding that a simple key could be wrong."
A public graduation ceremony, paid for by NCS, will be held for any students who did not graduate because of the errors, Jax said.
The mistake will mean lots of work for schools, said Kate Foate Trewick, chief academic officer for St. Paul Public Schools, where at least 25 students were kept from graduating.
School officials are trying to work with colleges to get those students enrolled. Meanwhile, fall high school classes already have been scheduled based on the faulty scores.
"I think it certainly shakes peoples' confidence in high stakes testing," Trewick said. "I suppose you could say it has dealt a blow."
The Minnesota foul-up follows other standardized test score errors and delays in reporting scores in Florida, Arizona, Tennessee and Michigan in just the last 12 months.
It's proof positive, the critics say, that no one test should keep any student from graduating.
"Twelve years of education cannot depend on only one test or only one answer," said Karen Hartke of Fair Test. It can't be that important or that valid."
In April, Minnesota Senator Paul Wellstone introduced a bill allowing students nationwide to graduate from high school, even if they haven't passed state-mandated basic skills tests in reading and math.
"We need to have high standards, but we shouldn't have over-reliance on a single standardized test," he said.
But educators are under tremendous pressure from parents and politicians to prove that their students have actually learned something and that no graduate is functionally illiterate.
Commissioner Jax, for one, explained, "These are basic competency tests. Our businesses demand that the diploma mean something."
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