Using a semi-spontaneous speech corpus, we present evidence from computational modelling of tonal productions from Mandarin-speaking children (4- to 11-years old) and adults, showing that children exceed the adult-level tonal distinction at the age of 7 to 8 years using F0 cues, but do not reach the high adult-level distinction using spectral cues even at the age of 10 to 11 years. The difference in the developmental curves of F0 and spectral cues suggests that, in Mandarin tone production, secondary cues continue to develop even after the mastery of primary cues.