The interpretation of data and construction and interpretation of graphs are central practices in science which, according to recent reform documents, science and mathematics teachers are expected to foster in their classrooms. However, are (preservice) science teachers prepared to teach inquiry with the purpose of transforming and analyzing data, and interpreting graphical representations? That is, are preservice science teachers prepared to teach data analysis and graph interpretation practices which scientists use by default in their everyday work? The present study was designed to answer these and related questions. The responses of preservice elementary and secondary science teachers, practicing science teachers, and scientists to data and graph interpretation tasks were investigated. This study finds that despite considerable preparation, and for many, despite B.Sc. degrees, preservice and practicing teachers do not enact the ("authentic") practices that scientists routinely do when asked to interpret data or graphs. Detailed analyses of written or videotaped answers on the tasks are provided. This report concludes that traditional schooling emphasizes particular beliefs in the mathematical nature of the universe that make it difficult for many individuals to deal with data possessing the random variation found in measurements of natural phenomena. (Contains 10 figures, 7 tables, and 49 references.) (Author/CCM)