A study of the total duration of sleep and its repartition during the 24-hour period was performed in 588 3 years old children entering kindergarten. The medical evaluation included physical examination, maturity tests, family interview. A detailed study of sleep schedule and school attendance was made in a group of 347 children. It appeared that almost 75% of the children are at school the whole day, a full time attendance without connection with the fact that the mother is professionally active or not. In these children, the absence of nap was not compensated by a longer nocturnal sleep and, very often, a state of chronic fatigue was noted. In conclusion, the modification of school rhythms is not to be considered as the unique end to achieve for the child: the family arrhythmia is to be taken into account as a matter of urgency, and an adequate information, clear and repetitive, needs to be widely provided.