Let me reiterate: that was the Washington STATE Supreme Court, making their decision based on the state constitution and state precedent. So we can't just hope this gets kicked higher and becomes the law of the land; education is a power reserved for state and local government.
And, as always, let me also reiterate that I'm not a lawyer; I just follow public ed case law.
I've seen several references to the 1917 amendment that prohibits public funds going to schools not controlled by local public authority:
All moneys raised by taxation in the towns and cities for the support of public schools, and all moneys which may be appropriated by the commonwealth for the support of common schools shall be applied to, and expended in, no other schools than those which are conducted according to law, under the order and superintendence of the authorities of the town or city in which the money is expended...(emphasis added)
If you read the whole of the amendment (or read any history of the Convention; see page 217), it's clear that it's directed at pariochial schools. That amendment was superceded by subsequent amendments (most having to do with higher ed), and, more importantly for our purposes, subsequent case law, including the case that involved Boston University running the Chelsea schools, in which the finding was that the authority could be delegated from that local authority, to wit:
The extensive supervisory controls that the school committee has over the university's performance of the city's educational obligations represents that kind of control, or more precisely right to control, that is an essential part of an agency relationship. Restatement (Second) of Agency Section 1 (1958). The university's agency is a public one because the university as an agent is fulfilling a public obligation, i.e., education of the youth of the city, McDuffy v. Secretary of the Executive Office of Educ., 415 Mass. 545 , 620-621 (1993), while subject to the control of a public entity as a principal, all pursuant both to its legislatively authorized contract and to the enabling act.(Emphasis added) Thus because BU was tied to the local school committee in authority and reporting requirements, they were sufficiently under local control for the courts.
Beyond that, to my mind, it brings us back to McDuffy.
The main thrust of McDuffy is the finding that the Massachusetts Constitution, when it makes education the "duty of legislatures and magistrates," is making it a shared responsibility between the state and local authorities. In the case of McDuffy, that means that funding of schools cannot simply be left to the local authority (the "magistrates"); the state (the "legislatures") must fulfill its responsibility to Massachusetts schoolchildren as well.
Is the reverse also true, one wonders? Is it the case that the "legislatures" cannot simply delegate their authority to a local board that does not in any way answer to a local authority? Unlike BU, charter schools and their boards are in no way responsible to local school committees. There is no local "magistrate" to which they answer. They answer only to the state authority, in particular, the executive branch through DESE. Is that, one wonders, constitutional?