This study aims to find evidence that validates an unprecedented scale assessing metacognitive knowledge about digital reading, developed for PISA 2018. More precisely, the study investigates whether the scale measures metacognitive knowledge about reading as opposed to ICT literacy. Data from the 37 OECD countries were used. The results show strong correlation between this metacognitive knowledge scale, reading performance, and two scales which have already been validated for measuring metacognition about reading. The scale is also significantly correlated with students’ interest, self-concept, and self-efficacy in reading. On the other hand, no correlation was shown between their use of ICT, and their interest and perceived self-efficacy in their use. The results provide evidence that the scale assesses metacognitive knowledge about digital reading rather than digital literacy. The results also demonstrate a strong correlation between the scale and reading proficiency.