We analyze here readings of the same reference text by 116 children. We show that several factors strongly impact subjective rating of fluency, notably number of correct words, repetitions, errors, syllables spelled per minute. We succeeded in predicting four subjective scores – rated between 1 and 4 by human raters – from such objective measurements with a rather high precision (R > .8 for 3 out of 4 scores). This open the way for automatic multidimensional assessment of reading fluency using calibrated texts.