The teaching practicum is probably the most genuine period of professional training at the teaching degree. The use of tools such as the teacher’s professional journal helps to reflect and systematize the experience of the teacher in training. This chapter includes the design of a mobile application to facilitate the use of the teacher’s professional journal through its digitalization in order to experience the benefits it brings as a tool that favors the teacher’s own practice and professional development. An analysis of the content of 20 teacher journals written by students of Infant Education at the University of Salamanca was made with the aim of extracting the main reflection topics. The result was a carefully produced indexing tree that has been used as an analysis tool in the NVIVO12 software for the study of qualitative data. The tree allowed extracting a significant and complete categorization of the teacher’s professional journal that makes possible its analysis and constitutes the starting point for the design of the prototype of the mobile application in a paper, which will be developed. The digitization of the professional teachers’ diary based on the most frequent topics of the teachers themselves in practice shows the relevance of the diary since it is based on a thematic index that arises from practice, not theory. This will favor its implementation both by teachers in training and by active professionals contributing to their professional development.