Purpose: The purpose of this paper is to investigate the long-term development of online research skills among lower secondary school students and how various factors such as teaching interventions and students' self-efficacy, attitudes, information and communication technology (ICT) activity and gender are associated with development. Design/methodology/approach: Two intervention courses were implemented to improve online research skills among 7th-grade students. In the follow-up test in the 8th grade, students' skills were measured in Web searching, critical evaluation of sources and argumentative use of Web information. Students' self-efficacy beliefs in online research, their attitudes toward learning, behavioral intentions in online research and ICT activity were surveyed by questionnaires. Findings: The main finding was that the effect observed immediately after the intervention in 7th grade did not last until the following year. A cluster analysis revealed six skill profiles characterizing strengths and weaknesses in students' performance in the subtasks of online research and indicated that many students suffer from poor evaluation skills. Self-efficacy beliefs stood out as a student-related factor associated with the development of online research skills. Originality/value: This study contributed to the pedagogy of online research skills. It indicates that small-scale interventions are not enough to enhance 7th-graders' online research skills. Students need continuous practice in different contexts during their school years. It is important to support students' self-efficacy to motivate them to develop their skills in all the subtasks of online research. This study also demonstrated the importance of follow-up studies in online research skills, as they have been rare thus far.