Andrew Dewey is an award-winning history teacher at Carnegie Vanguard High School in Houston. In 2011-12, he earned the top merit pay award that his school district gives out and had “most effective” teacher status through a controversial evaluation system that uses student standardized test scores. The next year, after teaching similar students in the same way, he went from being one of the district’s highest-performing teachers to one that made “no detectable difference” for his students.

Dewey is one of seven high-achieving teachers who, along with the Houston Federation of Teachers, filed a lawsuit in federal court in Texas late Wednesday alleging that the Houston Independent School District uses a badly flawed method of evaluating teacher effectiveness, known as the “Educational Value-Added Assessment System.” The teachers argue that the EVAAS is inaccurate and unfair but that it still plays a large role in determining how much teachers are paid and whether they can keep their jobs.

The method, generically known as “value added measures,” or VAM, is increasingly in use around the country — with the support of the Obama administration — after Michelle Rhee pioneered the method when she ran D.C. public schools several years ago. The result of this lawsuit could affect evaluation systems well beyond Texas.

“It’s dispiriting and insulting to be told I’m ineffective, a judgment that doesn’t mesh with my classroom performance or the time and effort I devote to my students,” said Daniel Santos, an award-winning sixth-grade social studies teacher at Jackson Middle School, another plaintiff in the Houston lawsuit.

The teachers say, among other allegations, that they are being evaluated on the scores of tests that do not assess the curriculum they are supposed to teach, that the formulas are incomprehensible, and that their Constitutional rights to due process are being violated because teachers cannot challenge the results. The suit further alleges that teachers’ rights to equal protection under the Constitution are being abridged because teachers with below-average scores find themselves receiving harsher scores on a separate measure of instructional practice. And it says that what the Houston administrators have decided is acceptable teacher “growth,” using the VAM models, is arbitrarily decided.

The use of the value-added system “in making high-stakes employment decisions has devastated employee morale,” Dewey said.

VAM purports to measure the “value” a teacher adds to student learning by plugging student standardized test scores into complex mathematical formulas that can supposedly factor out all of the other influences and emerge with a valid assessment of how effective a particular teacher has been. The method has come under growing criticism in recent years, with assessment experts repeatedly warning that it is an unreliable method of making high-stakes decisions about educators.

Houston school district officials, who implemented the value-added method in 2007, have repeatedly defended the system, including publishing a list of “myths” about it on the system’s Web site and touting its advantages.

“Nothing matters more to student success than teachers,” Houston officials wrote on their Web site. “Value-added measures how well schools and teachers are doing in accelerating the academic progress of their students. Value-added, when used with other measures, provides a more complete picture of performance.”

Last year, a group of Florida teachers and their unions sued their state over its VAM teacher evaluation system that measured teachers on the scores of students they never taught. This Texas suit argues that their value-added ratings have no connection to their actual performance and fail to factor in the outside influences that students bring into the classroom that affect how well they perform.

Dewey said that the formulas used to determine “value” are often not available to teachers to see, and when they are, they are “incomprehensible for an average person to understand.”

The latest warning from assessment experts about the use of VAM came earlier this month in a report by the American Statistical Association that slammed the method for use with salary or employment consequences. The association’s statement said that VAM results typically measure correlation, not causation, meaning that factors affecting student achievement other than the teacher are not caught.

Randi Weingarten, the president of the American Federation of Teachers, said that the obsession with standardized testing that has driven education policymakers to make standardized test scores the key metric of accountability for students, educators and schools, is bastardizing public education.

“This country has spent billions on accountability, not on the improvement of teaching and learning at the classroom level, and value-added models are the leading edge of this misguided effort,” she said.