Reading with phonetic writing systems is based in part on word shape recognition and part on context - as someone who visualizes words (you may see me exercising 'invisible' finger writing sometimes when struggling to recall one) I find this system suits me best
But - and this is a follow on from fonts - the amount of letter-spacing in text can also affect legibility

Just a thought - this is an interesting thread

Sorry I can't help you Spleen Cringe with any answers with regard to problems with a school, it's been a long time since I was in the system.