Who among first graders benefit from training in linguistic awareness, and what components of the linguistic awareness are most amenable to training effects? At the beginning of Grade 1 prospective at-risk readers (26 out of 117) were identified on the basis of very low phonological awareness. In the autumn term, they received practice in linguistic awareness. When compared to controls individually matched controls on phonological awareness, listening comprehension, and WISC-R scores, the intervention group showed a more rapid building-up of phonological awareness, especially phoneme-blending ability, as well as superiority in word recognition, spelling, and listening comprehension, which were sustained until the end of Grade 1. Reading comprehension could not be compared because 8 of the 26 controls did not read fluently enough to be tested. The half of the control group with cognitive delays, receiving normal special education instruction performed consistently worse than their matched pairs in the intervention group. The latter group showed development of phonological awareness, decoding, and spelling equal to that of the cognitively nearly average intervention group and their matched pairs in the control group, who received no additional support. These three groups, originally defined as at-risk readers, performed at the level of other preschool nonreaders at the end of Grade 1. In sum, the children with cognitive delays benefitted from training in linguistic awareness. The results underscore the importance of phoneme synthesis skills in beginning reading and spelling at least with regular languages.