Grapheme and syllable units have been shown to influence the dynamics of handwriting in adults and children, but the influence of morphemes remains to be clarified. We tested the ability of French-speaking adults and fourth and sixth grade children to process the morphological structure of words during writing. They were asked to copy three types of words on a digitizer: morphologically complex words, morphologically simple words matched for the bigram at the syllabic boundary, and morphologically simple words matched for the bigram at the morphemic boundary. Latencies were shorter for morphologically complex words than for simple words only in adults. Requiring individuals to process morphological structure increased the time taken to write the letter before a morphemic boundary in adults and sixth graders. In contrast, fourth graders wrote the letter before the syllabic boundary more quickly for complex words than for simple words. These results indicate that words are represented in a decomposed form in the lexicon, and that the morphological structure of words regulates the dynamics of handwriting.