In rhythmical tasks timing is an important control parameter. Precise timing implies both a small constant error and variability for reproduced movements. During development timing errors and variability decrease. In bimanual coordination variability of the relative phase is assumed to be a measure of the strength of coupling. In clinical studies enhanced variability is interpreted as a sign of neurological nonoptimality. In the present study variability of timing and strength of coupling in bimanual coordination is studied in clumsy and dyslexic children.