LOL.....Guess my kids went to different kinds of schools, then! Every year several newsletter notices come out during the school year requesting help with getting a student to or from school. Sometimes it is for a short period while a parent is ill or without a car for awhile, other times for just a certain day of the week, etc. Some other parent ALWAYS steps up to make sure this is taken care of, every time! In nearly 20 years of having my kids in these schools, I have never seen a notice have to be repeated with more than one request for help.
Also, no school my kids have ever attended would accept ANY kind of note written by a parent and sent in with a student. Several reasons there--the first one you have stated, too easy to get lost in the shuffle, second one is that there is no way to verify it came from the parent (kids can type notes themselves, you know!

) My point was that in either case, how hard is it for the parent to make a one minute phone call? NO PROBLEM at all, and solves a multitude of problems before they occur.