Reading comprehension is a complex and multifaceted process that consists in the extraction and construction of meaning from written texts. The structure of the texts, that is the relationships that are established between ideas and the way in which they are connected, is one of the factors that contributes to reading comprehension. Many students, despite being able to decode written texts, show difficulties in understanding what they read, especially when it comes to expository texts. According to several authors, students have difficulty understanding these texts because they deal with topics that are less familiar to the reader, contain specific vocabulary, don’t have the familiar structure of stories and are less studied than narrative texts in primary school. Given the difficulty of understanding these texts, which are widely used in different subjects throughout the school curriculum, our aim was to develop and evaluate the effectiveness of an intervention programme with the aim of explicitly teaching reading comprehension of expository texts to 4th grade students. We hypothesised that students in the intervention group would make more progress in reading comprehension of expository texts than students in the comparison group. We also asked the following question: will the intervention programme have an impact on the development of the reading comprehension of narrative texts? Participants were 103 4th grade students and 6 primary school teachers from 6 classrooms in public primary schools in Portugal. Three teachers agreed to implement the programme (53 students - intervention group) and three teachers carried out normal curricular activities (50 students - comparison group). The two groups were matched in terms of teachers' teaching experience and students' gender, age and cognitive level. The intervention programme, designed from an interdisciplinary perspective, was implemented by the teachers in their classes in 30 sessions of 1 hour, twice a week for 15 weeks. Texts with different structures were used: descriptive, sequential, comparative, problem-solving and cause-effect. Several strategies were suggested, such as activating prior knowledge and anticipating ideas, identifying new vocabulary, identifying main ideas, writing key words, creating schemes, monitoring comprehension. The activities were developed in a sequence of individual work, group work and general discussion. To evaluate the impact of the programme reading comprehension tests and participant surveys were used. Students were assessed on their reading comprehension of expository and narrative texts before and after the programme. The results showed statistically significant differences in the development of the two groups' comprehension of expository texts, with the intervention group developing more than the comparison group. No differences were found in the comprehension of narrative texts. Students considered that the programme enabled them to use different strategies to better understand expository texts. The teachers highlighted the improvement of students’ reading comprehension and the sharing of procedures by different groups of students. These results show the importance of explicitly teaching reading strategies to improve reading comprehension of expository texts. This intervention programme could be a starting point for other teachers to adapt to their school context to improve students' reading comprehension and academic success.

Keywords: Literacy, reading comprehension, primary school, intervention programme.