The purpose of this paper is to investigate the contribution of the electronic portfolio (e-portfolio) to improving students' performance and the sustainability of their knowledge. The method used is the experiment with an experimental and a control group, and a pair of pre and post measurements. The survey was carried out during the first trimester of the 2016-2017 school year and its duration was 30 teaching hours. The sample consisted of 40 pupils of the second grade of primary school in the city of Rhodes. The findings of the survey show that the students of the experimental group who used the e-portfolio scored higher in all assessments and managed to maintain the knowledge they achieved by scoring higher results in the second assessment of the material fifteen days later, compared to the students in the control group who used the traditional printed portfolio and scored lower in their performance ratings.