Good luck with the admin on that idea.
Getting three quarters of a million 18 year olds to turn up for voluntary work once a month? Who's gonna do all the paperwork, transport, checking in? Initial safety training, safeguarding training, risk assessments associated with have unqualified/untrained teens around? ?
What if they are already working for the nhs or a care home as a paid job?
What about the ones who need to work at weekends to get through uni?
What about the one's who no-one can get to school currently?
Are patients going to want a load of disgruntled teens wandering round hospitals and nursing homes?
It's pie in the sky.