The aim of this article is to determine to what extent definitions in a range of monolingual dictionaries satisfy the needs of the specific age groups for which the respective dictionaries were compiled. More particularly, the aim is to determine whether dictionaries for young children, more advanced children, and adult users offer definitions on the appropriate competency levels of these categories of dictionary users. The investigation is conceived as a case study. This case study involved participants in three age brackets: children from 8 upwards, children from 10 upwards, and adults from 18 upwards – all mother-tongue speakers of Dutch. These three groups were presented with the definitions from three Van Dale dictionaries: the Juniorwoordenboek , the Basiswoordenboek , and the Grote Van Dale – compiled for users aged 8+, 10+, and 18+ respectively. Three sets of tests were designed to investigate various correlations between the three groups of participants and the three dictionaries. The conclusion is that all three dictionaries ‘challenge’ their users. This has important implications for future research.