The relationships of different levels of phonological processing (sounds in heard and spoken words for whole words, syllables, phonemes, and rimes) to multi-leveled functional reading or writing systems were studied. Participants in this cross-sectional study were students in fourth-grade (n = 119, mean age 116.5 months) and sixth-grade (n = 105, mean age 139.7 months). Multiple Indicators and Multiple Causes modeling was used to analyze whether different levels of sound processing in heard and spoken words were correlated with each other and with multi-leveled reading or writing systems, and if so, which phonological skills explained unique variance in the reading or writing system. The models fit well at both grade levels for both reading and writing. All four phonological skills studied correlated significantly with each other and the latent factor for reading or writing. For reading, phonology for whole words and phonemes explained unique variance in fourth and sixth graders. For writing, at the fourth grade, only phonemes explained unique variance, but at the sixth grade level, syllables, phonemes, and rimes explained unique variance. Thus, the relationships between levels of phonology and reading were stable across grades 4 and 6, but developmental differences were observed in the relationships between levels of phonology and the leveled writing construct.