Predictions from theories of the processes of word reading acquisition have rarely been tested against evidence from exceptionally early readers. The theories of Ehri, Share, and Byrne, and an alternative, Knowledge Sources theory, were so tested. The former three theories postulate that full development of context-free letter sounds and awareness of phonemes are required for normal acquisition, while the claim of the alternative is that with or without such, children can use sublexical information from their emerging reading vocabularies to acquire word reading. Results from two independent samples of children aged 3-5, and 5 years, with mean word reading levels of 7 and 9 years respectively, showed underdevelopment of their context-free letter sounds and phoneme awareness, relative to their word reading levels and normal comparison samples. Despite such underdevelopment, these exceptional readers engaged in a form of phonological recoding that enabled pseudoword reading, at the level of older-age normal controls matched on word reading level. Moreover, in the 5-year-old sample further experiments showed that, relative to normal controls, they had a bias toward use of sublexical information from their reading vocabularies for phonological recoding of heterophonic pseudowords with irregular consistent spelling, and were superior in accessing word meanings independently of phonology, although only if the readers were without exposure to explicit phonics. The three theories were less satisfactory than the alternative theory in accounting for the learning of the exceptionally early readers. (C) 2014 Elsevier B.V. All rights reserved.