Summary: The Kairos project aims to investigate the problem of (de) synchronisation of biological times (chronotypes) in childhood and youth in relation to school times. It studies the  effects  of  student  chronotype  vs.  school  schedule  matches/mismatches  on  health  behaviours  (e.g.,  how  many  hours  students  sleep,  when  they  sleep,  eat,  do  physical  activity,  spend  time  outdoors  in  daylight)  and  learning  (verbal  expression,  spatial  structuring,  operations)  and  whether  alert-fatigue  levels  mediate  this  effect  alignments/misalignments  on  learning  (verbal  expression,  spatial  structuring,  operations)  and  their  mediation  by  alert-fatigue  levels.