On the first day of statewide exams this spring, Mike Hamernick, director of Northern Lights Community School, quickly realized he had a problem.

One by one that morning, his students came to his office at the charter school in the Iron Range community of Warba and handed him the same thing: a form, signed by a parent, opting them out of taking the Minnesota Comprehensive Assessments, or MCAs.

"I had a line of kids out the door, just [handing in] the forms," he said.

By the time he reached the end of the line, Hamernick had excused nearly all the school's students from testing: Out of about 50 students eligible to take the exams, only 10 sat for the math test and four for reading. The rest were put on a bus and sent to the town's community center, where teachers scrambled to put together an impromptu day of classes.

The sudden surge of test opt-outs isn't unique to Warba. Around the state, the rate of students choosing to bypass the state's largest standardized exams has been steadily rising for more than a decade. Though the overall number of students opting out statewide remains low — just under 2% declined to take the math test last year, and about 1.5% opted out of reading — there are a growing number of schools where more than half the students don't take the MCAs.

The trend poses a dilemma for school administrators. Federal law mandates that schools test at least 95% of their students, but it also allows states to grant students and parents the right to opt out — without any direct consequences. Meanwhile, school leaders are fielding growing concerns that the tests are becoming too large a part of the classroom experience, and that they are not relevant to students' post-high school plans. While many school leaders share some of those concerns, they also note that high opt-out rates muddy the picture about how well the school is doing. That's because students who don't take the test are counted as "not proficient" — meaning that even if a school is excelling by other measures, it could easily look like it's failing if enough students opt out.

At Hopkins High School, where close to half of the students eligible to take the MCA math test last year chose not to participate, that problem is on Principal Doug Bullinger's mind. "A very key piece of the puzzle is missing when people look at this data," he said.

All Minnesota public schools are required to administer the MCAs, which are designed to monitor schools' success in meeting academic standards and track gaps between student groups. Students in third through eighth grade take reading and math MCAs each year, and fifth through eighth-graders are also tested in science. In high school, students take a reading exam in 10th grade and a math test in 11th grade, plus science exams in years when they take specific science courses.

The state has long allowed students to opt out of the MCAs, though that fact hasn't always been well publicized.

In recent years, however, the Legislature has acted to ensure more people know about the option. Districts must now post the opt-out form on their website and include it in school handbooks.

In the Minneapolis School District, home to a handful of high schools with some of the highest opt-out rates in the state, Eric Moore, chief of accountability, research and equity, said school leaders are "very diligent" in letting parents know about the choice to skip the tests. Last year, 91% of students at Patrick Henry High School declined to take the math test, and 85% passed on the reading test. Close to two-thirds of students — or more — opted out of both subjects at South and Southwest high schools. Overall, Minneapolis' opt-out numbers declined last year, but there were still 14 Minneapolis schools with rates above 5%.

"We believe parents have the right to choose ... and our job is to also inform families about what those assessments can do," Moore said.

Opt-out rates can spike quickly through word of mouth among students or parents. That was the case in the Menahga Public School District, northwest of Brainerd, where in the 2017-18 school year, just two students bypassed the tests in a district with just over 1,000 students. Last year, the number of opt-outs surged across all grade levels, with more than half of the district's students declining to take the reading MCAs, and most of the same group refusing the math test.

Superintendent Kevin Wellen said he's heard various reasons from parents.

"Parents have expressed the concern we're over tested," he said. "Parents are concerned about test anxiety of their child, and about taking a one-day, one-moment snapshot."

Jeanne Flint of Brainerd said those are some of the reasons she started opting out her now-10th grader from the MCAs when she was in fifth grade. She said she's seen her children's schools increase the emphasis on the importance of the test, sending home messages about proper sleep and eating around testing time, and even instructing parents on what kind of peppermints to send with students to help them focus on the test.

"They're asking the teachers to live or die by the results of this test," she said, "and we just said: There's no benefit whatsoever."

In Minneapolis, Shannon Wadman has opted out both of her children. While her son and daughter, both diagnosed with attention deficit hyperactivity disorder, have thrived on other measures, she said they struggled with the dayslong testing periods for the MCA.

"I just feel like if we're going to put them through the grinder that is those kinds of tests, that it has to have some upside for them," she said.

In some districts, leaders say they are trying to do more to show both parents and students why the MCAs matter. In the St. Louis Park District, where 46% of high school students chose to sit out the math test last year, Silvy Lafayette, director of assessment, research and evaluation, said participation in the MCA reading test went up last year after the district stressed to families how the data from the tests help school leaders make changes in the classroom.

In Hopkins, administrators have responded to concerns about the MCAs being crammed into high schoolers' schedules alongside advanced placement exams, ACTs, and other tests by spacing out all of those exams over a period of months, rather than weeks.

Daron Korte, assistant commissioner for the Minnesota Department of Education, said officials try to communicate the importance of the tests on the form parents sign to opt out their students. That paperwork also notes that students will not be counted as "proficient" in the test results, something administrators say can have a cumulative effect on how it appears one school stacks up against another. In Minneapolis, for example, Moore said the surging opt-out rates at Southwest High School bumped it off the U.S. News and World Report annual ranking of top high schools around the country.

And perhaps of greater concern: When opt outs reach a certain level, the usefulness of the test score data becomes a serious question. Minneapolis has already reached that threshold, at least in some schools. A 2017 report from the Office of the Legislative Auditor found that the rate of opt-outs among Minneapolis high school students had already "reached the point where it is no longer appropriate to endorse the test results as a valid measure of districtwide student learning."

The report warned that if the opt-out movement continued to grow at the same rate, other districts would face the same problem.