This paper presents research about supporting primary school teachers in planning game based learning activities in different school subjects. Teachers can describe learning activities in the form of a learning scenario, which usually includes a list of learning outcomes, teaching methods and strategies, materials, and tools for achieving the learning outcomes. The process of designing a learning scenario can be challenging for teachers, especially those with a lack of ICT skills. Teachers should be familiar with the various ICT based teaching methods, strategies, contents and tools. Therefore, it is necessary to organize educational programmes to support teachers in acquiring appropriate knowledge and skills. The paper describes results of the study conducted during the education for primary school junior grade teachers organized within the Erasmus+ project GLAT that promotes development of algorithmic thinking using games. The aim of the study was to identify the level of participants’ knowledge and skills needed to design scenarios with game based learning activities for developing algorithmic and computational thinking among their students. Using questionnaires, the teachers’ self- assessment of familiarity with the terminology related to game based learning and possibilities of adapting and using digital contents, games and tools was determined as well as their self- assessment of progress made during the education. Teachers’ progress was realized to the greatest extent for elements related to games, learning scenarios, and applying Web 2.0 tools for learning activities. The results confirmed the effectiveness of the GLAT instructional model and showed that teachers need support not only through education, but also by providing ICT tools that will make the process of designing learning scenarios easier for them. Therefore, a future work in this direction is planned within the project Digital games and will include development of a web application for guiding teachers in the process of designing innovative game based learning scenarios.