Great article about Finland's education system.
For starters, Finland has no standardized tests. The only exception is what's called the National Matriculation Exam, which everyone takes at the end of a voluntary upper-secondary school, roughly the equivalent of American high school.
Instead, the public school system's teachers are trained to assess children in classrooms using independent tests they create themselves. All children receive a report card at the end of each semester, but these reports are based on individualized grading by each teacher. Periodically, the Ministry of Education tracks national progress by testing a few sample groups across a range of different schools.
As for accountability of teachers and administrators, Sahlberg shrugs. "There's no word for accountability in Finnish," he later told an audience at the Teachers College of Columbia University. "Accountability is something that is left when responsibility has been subtracted."