This study sought to identify the performance level of grade 3-6 students in the psychological processes of writing - lexicon, syntax and planning - and determine differences in neuropsychological and cognitive factors considering four socioeconomic levels in Callao, Peru. 804 grade 3-6 students were evaluated; the sample was subsequently subdivided into children who had and who did not have writing difficulties. Deficiencies in the mastery of basic (lexical) and advanced processes (syntactic and planning) as well as significant differences according to socioeconomic level were found. Significant differences were also identified in the mean scores of neuropsychological and cognitive factors favouring children 'without writing difficulties'. A relationship between neuropsychological and cognitive factors and the psychological processes involved in writing was discovered.