Europe. While participating in the realisation of the aforementioned projects, the partners had to mutually determine how they understood inquiry, what its characteristic features were, and which inquiry elements they wanted to develop/promote. Many of those projects used the definition of IBSE proposed by Linn, Davis and Bell (2004), who stated that inquiry is the: ' …intentional process of diagnosing problems, critiquing experiments, and distinguishing alternatives, planning investigations, researching conjectures, searching for information, constructing models, debating with peers, and forming coherent arguments. (p. 4)' . This definition is in line with the National Research Council (1996) guides, where students engaged in inquiry ' …describe objects and events, ask questions, construct explanations, test those explanations against current scientific knowledge, and communicate their ideas to others. (p. 2)' . Apart from the definition, invaluable contributions from Bybee (2000; should be noted, where among others, three descriptions of inquiry for teachers were provided and the 5E inquiry cycle was described. Those elements were used in almost all of the 7FP EU projects.Observing the history of the global IBSE implementation, one might think that both the process itself and its effects have been thoroughly studied already. However, despite the fact that education experts have extensively described their experience connected with teachers' training on the application of inquiry and have published the results of completed case studies, the extent to which training in the IBSE influences teachers' practices and students' achievement is still unclear (Capps, Crawford, & Constas, 2012;Ermeling, 2010). In this research, an attempt was made to examine the effect of the teacher training in the IBSE on their professional practices. The training encompassed by the research was carried out within the framework of the SAILS FP7 project. This project was realised in 12 European countries from 2012 to 2015, and during its realisation, more than 2500 of pre-service and in-service teachers participated in the trainings (Jönsson et al., 2015). The aim of the project was to prepare the teachers to teach through inquiry as well as have the confidence and competence in the assessment of their students' learning.The described research was carried out among in-service teachers participating in the project in Poland. In the Polish curriculum, the inquiry-based methods are not listed among the required/recommended teaching methods unambiguously, however, advised teacher/student actions and skills to be developed are in line with the competencies that are taught with IBSE (Polish Core Curriculum, 2008). The designed and implemented teacher education programme (TEP) was based on the framework developed within the SAILS project. The research carried out among the participants of the training was meant to answer a general question: "What is the effect of the training on the actual teachers' school practices?" The authors of the TEP an...