In this paper, we discuss the theoretical foundation and implementation of two alternative instructional courses that aimed to support the development of elementary school students' early algebraic thinking. Both courses approached three basic algebra content strands: generalized arithmetic, functional thinking and modelling languages. The courses differed according to the characteristics of the tasks that were used. The first course involved 'pure mathematical guided investigations' emphasizing scaffolding steps in pure mathematics contexts. The second course focused on 'applied open explorations' underlining more open questions in applied everyday contexts. The courses were compared in respect to students' learning outcomes. The findings, yielded from the analysis of pre-test and post-test data, indicated that the second course had better learning outcomes compared to the first. [Translation from English by Silvia Montero.]