The aim of this thesis is to analyse the relation between morphological awareness and morphologically based spellings, in Portuguese (European Variant). Two situations where the spelling is determined by morphology are examined: when the spelling flouts letter-sound correspondence rules (consistency in the spelling of stems in base and in derived forms), and when there is more than one spelling for the same sound (discrimination in the spelling of homophone suffixes). The studies used cross-sectional (studies 1, 2 and 6) and longitudinal (studies 3, 4 and 5) designs. Study 1 examines when children from grades 1 to 4 (6- to 9-year-olds; N = 805) can take advantage of morphological information that is made available to them, implicitly, through morphological priming. The primes are base forms that share the same stem with the targets and contain well articulated, stressed vowels. The target words and pseudo-words are derived forms that contain non-stressed schwa vowels. Although differently pronounced the latter vowels are spelled consistently with those in the stems of the base forms. Primes were either oral or oral plus written. Priming effects were assessed by comparison with a non-primed condition. No priming effects were detected in 6- and 7-year-old children. Both priming conditions produced a significantly higher level of correct spelling in children 8 and 9 years of age. Oral plus written primes allowed older children to use morphological spellings in both words and pseudo-words. These results suggest that older children can use implicit morphological information to spell schwa vowels morphologically. Study 2 examined the concurrent relations between morphological awareness and morphologically based spellings. Two issues were considered: consistency in the spelling of stems in base and derived (or pseudo-derived) forms and discrimination in the spelling of words and pseudo-words ending in homophone suffixes. Children from grades 1 to 3 (6 to 8-year-olds; N = 184) participated in the study. It was found that there was a significant relation between morphological awareness and consistency in the spelling of stems in Base - Pseudo-derived stimuli, after controlling for differences in grade and IQ. Mixed results were found for the spelling of homophone suffixes. The only significant prediction obtained was between morphological awareness and discrimination in the spelling of the words ending in the homophone suffixes '-esa'/ '-eza'. In Study 3, the relation between morphological awareness and consistency in the spelling of stems is analysed, longitudinally. Children from grades 1 to 4 (6- to 9-year-olds; N = 184) were assessed in three sessions (A, B and C) each separated by six months. The results showed that some of the measures of morphological awareness could predict consistency in the spelling of stems over periods of six and of twelve months, after controlling for shared variance with Grade and IQ. This is indicative of a strong link between morphological awareness and consistency in the spelling of stems. In study 4, the relation between morphological awareness and discrimination in the spelling of words and pseudo-words ending in the homophone suffixes '-esa'/ '-eza' is analysed. The suffix '-esa' forms nouns that indicate origin or provenance. The homophone '-eza' forms abstract nouns. The participants and design were the same as in the previous study. It was found that the younger children tended to use one spelling for the two suffixes. Then, when alternative spellings were used, their assignment was unsystematic. Systematic assignment was rare even in the older children. Some measures of morphological awareness in session B, accounted for unique variance in the discrimination scores measured in session C, after controlling for differences explained by grade and IQ. In study 5, the relation between morphological awareness and discrimination in the spelling of words and pseudo-words ending in the homophone suffixes '-ice'/ '-isse' is analysed. The suffix '-ice' forms abstract nouns. The homophone '-isse' is used in the subjunctive of some verbs. The participants and design were the same as before. Correct assignment of suffixes followed the same pattern of spelling phases as described in the previous study. Significant predictions were found between sessions A and B, B and C and A and C. Some of the morphological awareness measures strongly predicted discrimination scores, after controlling for the effects of grade and IQ. Study 6 examines the spelling of older children (Grades 5, 7 and 9) and adults (student-teachers and in-service-teachers (N total = 107). The aim was to find out when consistency in the spelling of stems and discrimination of homophone suffixes were eventually achieved and whether the adult participants were aware of the morphological rules that make discrimination predictable. Consistency in the spelling of stems was only systematic in grade nine. Discrimination of the homophone suffixes '-esa'/ '-eza' was not completely systematic after sixteen years of instruction (student teachers) Discrimination of words ending in the homophone suffixes '-ice'/ '-isse' was systematic by student teachers. Discrimination in the spelling of pseudo-words was not achieved. Spelling justifications were asked from teachers. These revealed that the knowledge of morphological rules was scarce, in complete or absent. This thesis provides first evidence that older children can use morphological information that is provided, implicitly, through priming. It also shows that achieving consistency in the spelling of morphologically related stems is a long process. Systematic discrimination of homophone suffixes is even harder. However, morphological awareness was generally found to contribute strongly to the spelling, and to predict spelling outcomes, even after stringent controls for grade and IQ. Further research is necessary to examine how children develop morphologically based spellings that cannot be anchored first, in a stable phonological matrix. These results also suggest that instruction with a strong morphological rationale might significantly enhance spelling development.