This study examined on-line processing of Swedish sentences in a grammaticality-judgement experiment within the framework of the Competition Model. Three age groups from 6 to 11 and an adult group were asked to detect grammatical violations as quickly as possible. Three factors concerning cue cost were studied: violation position (early vs. late), violation span (intraphrasal vs. interphrasal) and violation type (agreement vs. word order). Developmental results showed that children were always slower at detecting grammatical violations. Irrespective of age, participants were faster at judging sentences with late violations, especially in the younger groups. Intraphrasal violations were more rapidly detected than interphrasal ones, particularly in adults. Finally, agreement violations and word order ones did not differ. The hierarchy of cue cost factors indicated that violation span was the dominant one. A cross-linguistic analysis with French (Kail, 2004) underlines the developmental processing abilities and the interdependence between cue cost and cue validity.