This article argues that secondary school improvement in England, when viewed as a system, has become an impossible endeavour. This arises from the conflation of improvement with effectiveness, judged by a narrow range of outcome measures and driven by demands that all schools should somehow be above average. The expectation of comparable year-on-year examination results at age 15/16 in order to maintain standards of performance persists in uneasy tension with calls for continual improvement. The examination system acts as a limiter and sorter, with students, teachers and schools competing for grades that are constrained to a normal curve. GCSEs and their equivalents increasingly serve less to allow young people to demonstrate their achievements and more for holding schools and teachers to account. This has major implications for the justifiable desire that all our youngsters should learn in a "good" school, which adds value and narrows gaps. As some schools push forward in improving these measures, others inevitably roll back. Questions are raised regarding the sense and wisdom in maintaining the current situation, aimed at shaking off our normal-curve and above-average conditioning.