Timetable for school: 50% escape to head north (8)
I believe the answer is:
schedule
'timetable' is the definition.
(I know that timetable can be written as schedule)
'50% escape to head north' is the wordplay.
'50%' becomes 'sch' (I can't justify this - if you can you should give a lot more credence to this answer).
'escape' becomes 'elude' (synonyms).
'to head north' says the letters should be written backwards (I've seen 'heading north' mean this (in a down clue, letters travel north)).
'elude' in reverse letter order is 'edule'.
'sch'+'edule'='SCHEDULE'
'for school' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
(Other definitions for schedule that I've seen before include "List of times and places for events" , "Agenda" , "List of intended events and times" , "Syllabus" , "Timetable for activities" .)