With the current emphasis placed on ICT skills development in education, accurate information about how well students master these skills becomes invaluable. Despite the wide-spread use of self-report measures of ICT skills, their accuracy has been questioned. An analysis, on a large sample, of the heterogeneity in reporting behavior in the domains of ICT competencies is, as far as we know, missing; we fill this gap. We investigate the (in)comparability of self-reports of online communication skills (e.g., the using of social networks, data sharing) among two contrasting groups of students: (1) elite, high-performing grammar schools; and (2) economics schools (total N = 1,070 students, 17 secondary schools). Using the anchoring vignette method, we identify scale usage differences among respondents and adjust their self-reports for these differences. We show that grammar school students significantly underestimate their skills. Before the adjustment, grammar school students report significantly lower levels of online communication skills. After the adjustment, grammar school students have non-significantly higher levels of these skills. Differential academic demands thus might be a relevant factor in students' self-assessment of online communication skills. In practice, students' under-/over-estimation of skills might impact their access to ICT-related jobs and the effectiveness of educational decision-making in the ICT domain. We also show the potential of the anchoring vignette method to explain paradoxical negative relationships between self-reported skills and results on the achievement tests identified in the literature. Further research could explore this phenomenon in other domains of digital competence and among other student populations.