Authenticity is a term that has become ubiquitous within the field of science education, particularly when it relates to the practices of science. These practices are a key feature of science education reform documents in the US. However, a common definition of just what makes for the authentic doing of science is hard to come by and certainly lacks consensus. In this paper, the case will be made for a new framework building upon and updating prior conceptualizations that could be utilised by science teacher educators, science teachers, and science education researchers to classify the authentic nature of scientific work generally and that is performed in the science classroom specifically. The framework consists of three dimensions. These are the similarities between the practices that students engage in and those employed by professional scientists, the degree to which the activity is meaningful to the learner, and the extent to which the work is significant to others. Examples of classroom activities will be discussed in terms of these three dimensions. It is believed that the tools provided by this framework will have applications that will serve to encourage science teachers as they strive to implement authentic scientific practices in their classrooms.