French children program the words they write syllable by syllable. We examined whether the syllable the children use to segment words is determined phonologically (i.e., is derived from speech production processes) or orthographically. Third, 4th and 5th graders wrote on a digitiser words that were mono-syllables phonologically (e.g. "barque" = [baRk]) but bi-syllables orthographically (e.g. "barque" = "bar.que"). These words were matched to words that were bi-syllables both phonologically and orthographically (e.g. "balcon" = [bal.ko] and "bal.con"). The results on letter stroke duration and fluency yielded significant peaks at the syllable boundary for both types of words, indicating that the children use orthographic rather than phonological syllables as processing units to program the words they write. (Contains 2 tables.)