After Mayor Bill de Blasio rolled out a proposal to convert more than 90 struggling schools to community schools, fans of community schools — and they are legion — were ecstatic. Community schools speak to a broad array of progressive values, from the development of the whole child to the reclaiming of schools as centerpieces of neighborhoods.

But not all progressives were wowed, and the reaction to the proposal has been muted. The reason, in my view, is that the mayor failed to deliver a clear message about his goals for the school system — and that ambiguity may leave us with the same, traditional ways of measuring success by test scores and graduation rates.

Our politicians must walk a fine line in articulating what the purpose of a public K-12 education is and what outcomes we seek to achieve. As David Labaree has argued, three goals have long been in tension: preparing young people to be actively engaged citizens; sorting them into the varied positions necessary for our economy to be competitive; and enabling young people to advance beyond the achievements of previous generations.

Remarkably, the mayor’s address sidestepped any articulation of what the goals of his administration are for our schools. We can glean a bit from the text of his speech about what he and First Lady Chirlane McCray sought for Chiara and Dante, their two children educated in New York City public schools, but the goals are impossibly vague. The Mayor and his wife worried about how they would educate their children “for adulthood,” and he wishes to ensure that every child receives “the education he or she needs to succeed in life.” Students must be prepared “for the jobs of today—which increasingly require skills previous generations could not have dreamt of,” and our renewed schools should “make a real difference in student achievement.”

None of this provides real guidance on how we would know if the system is working as intended. In the absence of a clear statement of what students should know or be able to do, how are we to judge if any one school is struggling — and therefore a candidate for special help — or if a struggling school is on the road to recovery? Minus an alternative framework for what counts as success, stakeholders are likely to rely on the same things we’ve been using, and complaining about, for years: standardized test scores and graduation rates.

To be sure, the mayor’s intent to dial down the use of these measures is commendable. High-stakes accountability systems can distort the meaning of test scores and graduation statistics, as we’ve seen across the state and in New York City over the past decade. But those statistics are likely to remain the default measures of school success, crowding out the many other goals and outcomes that we can collectively imagine, if we don’t offer clear ideas about how else schools should be judged.

The mayor’s ambiguity about the goals of the system extends to his proposed solutions.

The hallmark of community schools is their effort to dismantle boundaries between the school and the community, locating a variety of social services designed to promote the healthy development of children — health care, counseling and mental health, and nutrition, to name a few — within the school. The problem that community schools address is children’s physical and psychological well-being, both of which are prerequisites to readiness to learn.

But schools can struggle for other reasons as well. They may have a dysfunctional culture in which the principal and teachers don’t rally around a core mission and are unable to work together productively on curriculum development and instructional practices. If this is the problem, community schools aren’t the appropriate solution. And if a school is already struggling to organize effectively to manage basic instruction, it may be unwise to saddle it with the additional responsibilities associated with a well-run community school.

A better way to assess a school’s functioning would be by using the capacity framework released by the Department of Education last month: measuring for rigorous instruction, collaborative teachers, a supportive environment, strong family-community ties, effective school leadership, and trust. These concepts have been successful in predicting which schools make progress in student test scores and attendance. As the city develops indicators for those concepts, a struggling school’s profile may result in targeted support in the areas where the school has fallen behind.

But a school’s capacity is still just a means to an end, and doesn’t help identify what we want students to learn. That remains a matter of values — values that the mayor has yet to communicate clearly.