Artiklen analyserer kvaliteten af tre reforminitiativer rettet mod folkeskolens naturfag: revisioneraf naturfagenes malsaetninger i folkeskolen, tilskud til folkeskolelaereres naturfagsdidaktiskeefteruddannelse og aendringer i grunduddannelsen til folkeskolelaerer i naturfag. Reforminitiativerneanalyseres ud fra laereres muligheder for at investere ressourcer i reformerne. Analysen viser at laerernehar haft varierende grad af indflydelse pa implementeringen i skolens hverdag. Dette har skabt enubalance mellem laerernes og andre aktorers roller og investering af ressourcer, og dermed forringeskvaliteten af reformernes implementering. The quality of three reform initiatives in science education in Denmark isanalyzed: reform of the central aims, reform of in-service teacher trainingprogrammes and reform of pre-service science teacher training. The analysisfocuses on teachers’ possibilities and constraints to invest resources in implementingreforms. The analysis indicates that teachers have had various degreesof possibilities for implementing the reforms. This situation has created animbalance between teachers’ and other actors’ investments in resources, whichreduces the quality of the reforms.