Leaders in the Minneapolis Public school district said this week that the accuracy of this year's standardized test scores for some of their schools was damaged because a significant number of students opted out of taking the tests.

This year's Minnesota Comprehensive Assessments data, released Thursday, shows that Minneapolis high schools in particular will have a hard time relying on the tests to assess the progress of their students in meeting achievement goals.
The data also show that opting out is a growing -- although still small -- trend elsewhere, as well.
In the 2015-16 school year, 94 out of every 10,000 students statewide refused to take the math tests, up from 3 per 10,000 just 4 years earlier. A lower rate of students refused to take the reading tests, but that has also risen sharply from four per 10,000 students to 74 per 10,000.
Breaking it down by grade level shows that 10th graders (reading test) and 11th graders (math test) have the highest opt-out rates.
In addition to opting out, other students don't take the tests because they are absent that day or have a medical exemption. Some students don't complete the exams and other exams are found to be invalid. But the number of students not taking the test for those reasons is far lower than those who simply choose not to take it. Opt-outs account for more than half of the cases for not taking the reading or math test.
State education commissioner Brenda Cassellius said the number of opt-outs might actually be higher because the data doesn’t account for students who refuse to take the test on the spot. The opt-out numbers only count those who alerted the school ahead of time. 
“I think our numbers are even larger,” Cassellius said.
Less than 2 percent of students statewide don’t take, or don’t complete, the tests, either because of opting out or these various other reasons.
State and federal law requires that schools see 95 percent participation on state accountability exams. The implications of not meeting that standard are still unknown as the state works to rewrite its laws to comply with the new Every Student Succeeds Act, which recently replaced No Child Left Behind.
There were 65 schools in the state that did not have that 95 percent participation rate. The numbers of students refusing to take the test might vary by grade level. For example, 32 percent of 11th graders at Hopkins Senior High opted out of the math test, but only 3 percent of the 10th graders opted out of the reading test.
Minneapolis high schools, particularly Southwest and Henry, have very high refusals for both math and reading. 
At Southwest last year, 95 percent of the 11th graders opted out of the math test. As a result, only 12 students were tested; five of them scored in the range that is considered proficient (42 percent).
Four years earlier, nobody opted out of the math test and 202 out of the 354 students tested were proficient (57 percent). Such a small number of students being tested really throws that 42 percent into question statistically.
Read the Star Tribune's story about this year's test results, and search results for your school here.

Data Drop is a weekly feature that uses data analysis and visualizations to explain, surprise, inform and entertain readers on topics relevant to Minnesotans. Do you have an idea you'd like us to explore? Contact MaryJo Webster