This work presents a constructive approach to the process of fixing a sequence of meetings between teachers and students in a prefixed period of time, satisfying a set of constraints of various types, known as school timetabling problem. The problem is modeled as a bi-objective problem used as a basis to construct feasible assignments of teachers to classes on specified timeslots. A new representation for the timetabling problem is presented. Pairs of teachers and classes are used to form conflict-free clusters for each timeslot. Teacher preferences and the process of avoiding undesirable waiting times between classes are explicitly considered as additional objectives. Computational results over real test problems are presented.