The research that studies the development of the structure of primary school students' written arguments on science issues is particularly limited. The present paper aimed to study the effect of a teaching intervention for electric circuits on the structure of primary school students' written arguments. Instructional material was developed based on the constructivist approach to learning with the use of science and engineering practices and was implemented with 34 students aged 11 years old. The research data included the 340 written arguments the students produced in their attempt to answer the questions included in a questionnaire, they were given before and after the teaching intervention. Data analysis was carried out by classifying the sufficiency of the components of the arguments into levels. The analysis showed that the teaching intervention significantly contributed to improving the structure of students' written arguments.