School costs can’t be allowed to grow faster than the income of the taxpayers.

That’s true of all government spending for every societal need. But when it comes to building roads, housing or protecting the environment, you don’t really hear a roar of influential voices making a perpetual argument that no matter how much we spend, it is nowhere near enough.

With schools, you always do. But this year Gov. Andrew M. Cuomo is trying to change that.

School administrators and teachers unions say, yearly, that there must be more money. Resistance becomes a moral argument; it’s practically considered a crime against our children.

Cuomo says underfunding isn’t the problem. On Long Island, where the average per-pupil spending is, according to the Empire Center for Public Policy, $26,232 per year, his words ring true. Even the statewide average of $22,718, easily the highest in the nation, seems to indicate a shortage of spending isn’t the issue.

The problem, according to Cuomo, is that we are not getting our money’s worth. Exhibit A is an education culture and bureaucracy that somehow manage to rate 98.7 percent of high school teachers as effective. Yet only 38 percent of high school graduates are found to be ready for college or careers.

In exchange for a bump in funding, Cuomo wants some things done to get better results. These include a tougher teacher evaluation system, an easier path to terminate ineffective teachers, greater ability to close or transfer control of failing schools, less emphasis on seniority and more merit pay for the most successful teachers.

In this brewing battle, taxpayers, and parents in particular, will have to pick sides. They will have to decide whether they are with Cuomo and like-minded reformers, or with an education establishment and union leadership that will always fight tough evaluations and budget constraints.

The weapon in the battle will be state aid to schools. The hostages will be the children: their extracurricular activities, curriculum options, class sizes and everything else that costs school districts money.

Cuomo’s play is this: He says if he gets what he wants in terms of more objective standards-based teacher evaluations, tighter tenure requirements and an easier path to firing failing teachers, districts will get a 4.8 percent increase in state aid, or about $1 billion more than last year. If he is thwarted, schools will get an increase of only 1.7 percent, or about $300 million, in line with the increases in budget for all state operations.

Educators who fight the reforms will, in effect, be fighting more funding of their schools.

This will play out in front of a Democrat-dominated Assembly that depends heavily on union support. And it’s going to play out in front of a just-barely Republican Senate that, while it supports schools, has made easing the burden on suburban taxpayers an even higher priority.

Over the past two years, teachers unions succeeded in rallying parents against reform by marrying their complaints about teacher evaluations to parental fears of Common Core. Now, the backlash against the new curriculum seems to be fading and the loyalty of the concerned parents who are also strapped taxpayers is up for grabs.

Another divide pits the youngest teachers and the best teachers against the establishment: the unions despise incentives and reward seniority, but great teachers support incentives like Cuomo’s $20,000 state bonuses, and young, energetic teachers are tired of seeing all the contract perks go to older colleagues.

The districts will get more money if parents back Cuomo. More important, education will get needed reforms if parents take Cuomo’s side. No one will benefit if the parents back the teachers unions — except the teachers unions.