What percent of Wisconsin students graduated high school in four years in 2016?

The Department of Public Instruction isn't totally sure.

And now, wrong information is locked into the department's public-facing online data portal, state officials said Wednesday.

The problem stems from a major data-reporting error, and it's resulted in some embarrassing inaccuracies for districts in 2015-'16, such as Waterford Union High School's 1% graduation rate. And Mount Horeb's 2.3% graduation rate.

The previous year, Waterford Union and Mount Horeb graduated 94.6% and 98% of students, respectively.

The error means it's impossible to know if the 88.2% statewide average four-year graduation rate for 2015-'16 is actually correct.

"It could be up or it could be down, and we don't know," said Tom McCarthy, DPI spokesman.

The statewide four-year average graduation rate was 88.4% in 2014-'15, and 88.6% in 2013-'14.

McCarthy said the error occurred because DPI has moved all of its student data into a single system connected to the Wisedash portal. Graduation data was the last item the DPI collected under the old system before the server was shut down, McCarthy said.

School districts can use different vendors to track their student data. In some cases, McCarthy said, graduation rate data individual districts entered did not flow accurately into the new tool and nobody received a warning that anything was amiss. In other cases, people simply input the data incorrectly.

In the past, when the data set went up behind-the-scenes, state and district officials could review the numbers and fix any errors before the data was released publicly.

But this year, when about 20 districts reported to DPI that their 2015-'16 graduation rates were incorrect, it was impossible for the state to change the numbers because the old system was already closed.

The good news: McCarthy said the state will work with districts to correct all the graduation rate errors before report cards for schools and districts are released in the fall.