Charter schools are public schools that operate under a contract ("charter") with an authorizer — a school district, university, or state board — and receive public per-pupil funding while operating outside traditional district governance. The charter movement began in Minnesota in 1991 and has grown to enroll roughly 7% of US public-school students.
Quality varies widely. Some networks (e.g., KIPP, Success Academy, Uncommon Schools) have produced strong results, particularly for low-income students of color in urban districts. Others have underperformed traditional public schools or closed for academic or financial failures. Authorizer rigor matters significantly.
Debate centers on funding effects on traditional districts, accountability and oversight, teacher unionization, special-education enrollment patterns, profit-motive concerns about for-profit operators, and what counts as fair comparison of outcomes.