The number of out-of-school science programs, which refers to science education at outside school environments, is gradually increasing. Although out-of-school programs are generally considered to be important for the development of pupils’ science knowledge and skills, more evidence concerning the learning effect of these programs is needed. In the present study, we explored whether different degrees of implementation of a connected in-school and out-of-school science program affect pupils’ cognitive science skills in relation to teachers’/instructors’ support. We used a multiple case study design with four cases comprising three different degrees of program implementation: optimal, intermediary and marginal. The cases comprised pupils of upper grade elementary school classes, their teachers, and the instructors of the out-of-school activity. The effect of the program was measured by coding pupils’ performance with a scale based on skill theory, and by coding teacher’s/instructor’s support with the Openness Scale. The data was gathered from microgenetic measurements over time, corresponding with an in-depth analysis of the process of change in naturalistic conditions. We found the highest learning effect in the optimal program implementation, which indicates that it is favorable to implement the complete program, and train teachers/instructors to use open teaching focused on conceptual understanding.