Value-added assessment uses statistical modeling to compare student test score gains from year to year, allowing comparisons between schools and teachers even with different student populations. It can show whether individual students or classes achieved expected, less than expected, or more than expected progress based on prior scores. Looking back over multiple years, value-added assessment can measure the long-term impact of teachers and schools. It aims to provide longitudinal growth data for each student and level the playing field by focusing on individual student progress rather than overall performance or demographics.