<p>In today’s data-rich society, the ability to work critically with data is a key competence for education and informed citizenship. Although research has often focused on university students or workforce readiness, less is known about how younger learners engage with data literacy and which competencies pose the greatest challenges. Addressing this gap is important for guiding curriculum reform and teacher preparation, as data use is increasingly emphasized as a transversal skill. This study examined the data literacy of Slovak students aged 12–14 across four domains defined by Ridsdale et al. (2015): collection, management, evaluation, and application. A standardized test of 19 items was administered to 795 students from 24 schools. Analyses included descriptive statistics, non-parametric comparisons, correlations, and regression models. Results show that students performed best in Data Evaluation, particularly in interpreting graphs, while Data Management was their weakest area. The domains were interconnected, with Data Evaluation functioning as a central hub supporting both management and application. Gender differences were modest, with girls showing slightly higher achievement in selected domains, and grade-level comparisons indicated gradual improvement with age. These findings suggest the need for instructional approaches in secondary science education that provide students with authentic opportunities to collect, manage, interpret, and communicate data, supported by curriculum design and teacher preparation.</p>