Creation of models is becoming an important part in the education of informatics besides algorithmization and programming. The L-systems are an appropriate example concerning use of computer science while modeling real world. In this paper we describe a proposal of teaching of plant's growth modeling by the L-systems at a high school. The main idea is an algorithmic creation of model of a real object -a plant. The L-systems and their graphic representation allow us to describe and to study phenomena that relate to the growth and the development of the plants using tools of the discrete mathematics and the computer science. We used the revised Bloom´s taxonomy for the determination and the assessment of educational objectives. The analysis of the outcomes of our research has shown that the creation of a graphical plant´s model in a programming environment substantially enhanced the development of cognitive skills in pupils.