do you have a schedule prepared for a primary school?
See the attached files. There are two initial files and their respective solution timetables (_data_and_timetable.fet). If you generate on the _data_and_timetable.fet, you get always the same solution, instantly.
These files are from the official FET examples set and I think they are for primary schools. The Brazil one was converted from an aSc Timetables (a competing program to FET) example by another user a long time ago.