I am here because I have completion check box pre filled and can not make them 'clickable' Anyway I came across this which might help you.
In your chose course
Course admin>course completion> ConditionManual Self Completion
In your chose course
Course admin>course completion> ConditionManual Self Completion
Then back into y our course and add the block 'Course completion status'
No idea if this will work but its worth a try!
.......and if anyone know why my completion boxes are pre ticked and not active I would appreciate suggestions.