Orthographic processing is a key predictor of reading fluency in good and poor readers in a transparent orthography

•Orthographic skills are the strongest predictor of reading fluency in Russian.•In good readers, orthographic skills also contribute to fluency via unitization.•Phonological skills make no direct contribution to reading fluency.•In good readers, unitization, but not decoding, is a predictor of reading fluency.•In poor readers, decoding, but not unitization is a predictor of reading fluency.