The Education Review Office says too much assessment is causing stress and anxiety for students at some secondary schools.
It published reviews that showed many primary and secondary schools were falling short on ensuring their students' well-being.
The reviews found most primary schools did well or reasonably well at promoting well-being, but 20 percent relied too much on behaviour management and a few schools were overwhelmed by well-being issues.
The ERO said only 11 of 68 secondary schools it reviewed were doing a good job at promoting student well-being.
It said 39 had a variable approach to well-being, 14 were challenged and four were too overwhelmed to promote or respond to student well-being.
Students in all of the secondary schools reviewed were found to be experiencing a very assessment-driven curriculum and assessment anxiety.
The review said in many secondary schools the only people who understood the competing demands on students were the students themselves.