-—Since it is now clear that school attendance is neither necessary nor sufficient for this purpose-—
I would ague that is not a true statement. The fact that some parents are capable and determined and have the disipline to home school does not mean that all can or will.
Further absent the compulsion many would chose to quit or nor atend or lay out. Some parentw would just not care.
Although in some locations a highschool diploma is a worthless paper actually signifying nothing, it is an actual benchmark for employers evaluating potential workers.
I would argue that it is a true statement. Do people learn to read, write, and calculate without attending school? Yes, many do. Do people attend school but not learn to read, write, or calculate? Yes, many do.
Therefore, “school attendance is neither necessary nor sufficient” to produce citizens with adequate basic education.
Whether, on the whole, the current system is better than an alternative - even if the alternative is no mandate at all - is an entirely separate argument.