None of the voucher systems I've heard of abolish the public system. It simply gives parents and students more choices and actually forces the public system to compete instead of continually beg for more funding that ultimately goes into the pockets of administrators instead of teachers and resources for students.
I do not see what public education advocates are fearing here. If their systems are so amazing and essential than surely the private sector can do no better, right? This will force school systems to become more lean from an administrative point of view.
One issue is that good quality education isn’t linear in cost. A school with 5 students may have lower overhead but will lack amenities that enable better learning, eg athletic infrastructure, libraries, etc. We provide public versions of those things, but then we’re back to funding parts of the education system with public levies. Furthermore there are some economies of scale that a public system enables, particularly around equitable access. For instance, I read somewhere that the postal service loses money delivering to remote areas. But given their mandate to serve all Americans, those in remote areas have access to a postal service. A private model would not likely serve those people well, if at all.
The most important thing for young student success is small class size. These concerns you have are more applicable for older students but I’m sure there’s ways to mitigate them.
I do not see what public education advocates are fearing here. If their systems are so amazing and essential than surely the private sector can do no better, right? This will force school systems to become more lean from an administrative point of view.