Iowa's student achievement remains "largely unchanged" after implementing the state's teacher leadership system, a school reform designed to foster better instruction and improve student learning through a coaching model.

The $157 million-a-year, state-funded program has had little influence on student achievement in reading and math in its first few years, and in some areas saw student results decline, according to a report released Tuesday by the governor's office.

Yet perceptions of the teacher coaching program are largely positive among educators, who cited improved instruction and better working environments, according to the 99-page report.

The independent review by the American Institutes for Research included an educator survey as well as an analysis of student test results before and after the coaching system was implemented.

Student achievement grew in grades 6-8, but declined in grades 3-5 and had no significant changes in grades 10 and 11, the review found.

The report also found some declines in student achievement among low-income students, those learning English and those receiving special education.

"There is work to do, and our administration will continue to look for ways to ensure Iowa’s teacher leadership system is even more effective," said Gov. Kim Reynolds.

A previous report on the TLC system also found mixed results: last year, state leaders urged schools to stay the course, and promised the system will show results "over the long-term."

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Iowa's teacher leadership system is designed to elevate the profession by promoting more than 25 percent of teachers into leadership roles, which are supplemental, part-time or full-time positions.

Teacher coaches then collaborate with other educators to improve classroom instruction and student learning. Districts take different approaches to the leadership positions.

The program was rolled out over three years starting in 2014-15 and is now in each of Iowa's 333 school districts.

"Iowa’s teacher leadership system sets the stage for our educators to prepare students for success," said acting Lt. Gov. Adam Gregg on Tuesday.

About 87 percent of teachers and 93 percent of administrators believe the teacher leadership system improves instruction, the 2017 report found.

A large majority of teachers and administrators believes it has a positive impact on their professional work environments.

Teacher coaches also appear to help with retention, potentially staving off what some warn is an impending teacher shortage.

About 78 percent of teachers who said they are looking forward to returning to their school next year said that teacher coaches impacted their desire to return.

The teacher initiative "is about supporting teachers to do their best so that our students can do their best,” Reynolds said.