The paper presents a research that aims at determining whether integrated and constructivist outdoor learning program "Danube – a classroom on the water" has positive effects on the immediate short-term and long-term  retention of the studied content in relation to learning in the classroom through regular teaching methods.  Therefore, we examined students (N = 120) from 4 classes of the third grade of elementary school. The experimental group consisted of 60 students who participated in the outdoor learning program "Danube - a classroom on the water ", and the control group of 60 students who were taught the same content in the classroom through regular teaching methods. In order to determine the statistical significance of differences between the experimental and control group, as well as the differences in achievement on the tests immediately after learning and four months later, we applied the analysis of variance (ANOVA), a single factor with unrepeated subjects ANOVA and parameters for determination of statistical significance. Natural and social environments outside the classroom provide an excellent opportunity for the integrated approach to teaching and application of various learning and teaching strategies. In this sense, the results of this study point to the benefits of the integrated outdoor learning in terms of knowledge retention. Thus, the necessity to increase teaching hours outside the classroom in schools in Serbia is reccommended in order to improve the quality of students’ knowledge and to create a favourable social climate for sustainable, interdisciplinary study and the use of the Danube as a source, means and objective of both teaching and learning.

Key words: The "Danube – a classroom on the water," outdoor teaching, integrated curriculum, constructivist learning, knowledge retention