In order to distinguish the various roles reduplication may have in child language development, we decided to code and analyze all Reduplicative Productions (R.P.) in the longitudinal data of a child. We used the longitudinal case-study of a monolingual French little boy in spontaneous interaction with his mother. The child was videotaped and audio-recorded between the ages of 0;2 and 1 ;10, in his home for half an hour sessions every two weeks. We made a systematic analysis and compared the occurrences of single phonemes [m] and of strings of reduplicated phonemes [m m m] in similar contexts. The results of our study indicate that after the age of one-year-old, there are three different types of reduplication in our data: 1. At around one year old, the child starts using reduplication to emphasize what he says. We can call this “the expressive” function of reduplication after Bloch (1921). That function is paralleled in adult language as in English when we say “he's a big big boy”, or in a more grammaticalized way in Yoruba “mura kia kia” (to get prepared fast fast) 2. The child uses another type of reduplication with units separated by a 70-centisecond pause to enumerate referents. Reduplication has an iconic quality. This could be a pre-grammatical process and prepare the child to the use of the plural. This function of reduplication resembles the plurality value of reduplication which is often grammaticalized in some adult languages. In Kannada (South eastern Asian language) “manne” means house and “manne manne”, each house, in Pangasinan (Austronisan) “manok” means chicken and “manok manok” chickens. 3. A few months later, in certain contexts, the reduplication of syllabic [m m] or vocalic sounds, [i i], enables the child to establish a rhythmic pattern similar to the signifier (composed of two syllables, such as “ papa ” or “ maman ”) which can be used for all kinds of referents. The child produces two identical sounds [i i] or [u u] separated by a very short pause. This configuration could be viewed as a single, lexical type, unit. Reduplication could therefore be a tool used in the construction of the lexicon in so far as it enables the child to produce a general pattern, which stays the same for all referents. The reduplicative productions with a referential value which enable children to build, enrich their lexicon may be more specific to language acquisition, but, probably under the influence of this dynamic acquisition device, a certain amount of lexical words in various languages consist in reduplicated syllables. Examples in French child language : koko (œuf/'egg'), pinpin (lapin/'rabbit'), toto (bateau/'boat').