Students' perceptions can influence their performance in writing. In the Portuguese context, the number of studies on this subject is still small and has not provided a clear overview of typical perceptions, for example, of students by year of schooling. Even more significant is the gap in international and national research on the relationships between students' self-perceptions and their performance in writing, mainly when mediated by Information and Communication Technologies (ICT). In this sense, this descriptive-correlational study focused on study the correlations between 4th grade students' perceptions (n=338) regarding writing knowledge, attitudes, and self-efficacy in writing and their writing performance. The results of this study allow us to state that, in general terms, there are more positive perceptions of students' attitudes and self-efficacy in writing with ICT than those without using these tools. Even though students' perceptions may be different from their performance, it was found that their attitudes were more optimistic than their perceptions of knowledge and self-efficacy in writing. Understanding observed differences is essential for educational professionals to know their students' perceptions, better adjust their pedagogical practices and select the pedagogical tools for each stage of the writing process.