As noted above, schools comply with a form of HIPAA law regarding privacy of medical records.
In our school(s), we have one school nurse (part time) for every 4 buildings...so less than 1/2 day per building per week. So really, they are plan managers. The REAL people in charge, are the school secretaries in every building (in more ways than just health issues). Most buildings, they are the ones who do administration of medication, documentation, etc. They also keep all the meds, files and document records under lock and key.
So are you saying your child's stuff is laying out open for anyone to see or that lots of folks actually go looking for it on a regular basis?
Having had diabetics before, I would say the only folks who have regular access to the daily testing is the school secretary and the school nurse. Even classroom teachers don't know the specific numbers. Frankly, I'm not even sure why they would or should care about it except that they don't want your kid going into shock or such.
How often do your kids need to test at school? Would a pump be an option for them to help w/regulation (and the privacy issue)?