Context: Statistical graphs are pervasive in the media and professional settings and therefore its understanding is a relevant component of statistical literacy. Objectives:The aim of this research was to assess the understanding of statistical graphs achieved by Chilean children when finishing their primary education and how much of this understanding is maintained one year later. Design: To achieve this aim, we built a comprehensive questionnaire which takes into account a previous analysis of the Chilean curricular guidelines and textbooks for primary education. The main variables characterizing graphical competence in the literature, and recommendations from experts in statistics education were also considered in the construction of the questionnaire. Participants and setting: The sample is intentional and is made of 745 6th and 7th grade students in Chile. Data selection and analysis: The responses to this questionnaire are analysed quantitatively and qualitatively. Results: We inform of the task difficulty according to the different variables in the questionnaire and the average reading level of statistical graphs achieved in the grades. We also inform of the main difficulties related to the different graphs and activities proposed in the questionnaire. Conclusions: We conclude that hat the students learnt by the end of the 6th grade is remembered one year later, dot plot and pie charts were the most difficult graphs, building of graphs was difficult when the frequencies were not provided and few children attained the upper level of reading graphs.