To get a sense of what is likely going to happen to many of the 3.2 million teachers employed in America’s classrooms who don’t teach core subjects such as reading, math, science, history and foreign language, consider the experience of a corporate lawyer who just spent a few days teaching business law at a high school in the D.C. suburb of Loudoun County.

Volunteering as part of a nonprofit that instructs teens on the ins and outs of the nation’s legal system, this lawyer spent time teaching a class of students about that lovely thing called torts and lawsuits. During those sessions, she finds herself getting into a lively Socratic discussion with her students, many of whom may not know about such terms as liable but definitely know about the spate of suits over statements made on Facebook and Twitter.  The kids are engaged, interested, and want to learn more. Theoretically, she is supposed to jointly teach with a full-time instructor who also handles high school electives in computer science and the golf team. But, in all honesty, the teacher can barely tell the difference between a summary judgment and a jury verdict, and barely considers his students — most of them Latino and black — capable of learning about any aspect of civics. In fact, instead of using the engaging course options offered by the nonprofit that would further immerse kids in learning — the teacher hands out worksheets on vocabulary terms.

At the end of her work, the young corporate lawyer figures out a few things — and that’s beyond realizing that the high school’s principal brought in the program in order to essentially keep this tenured and expensive laggard from doing any further damage to her students. The first? She enjoys every aspect of teaching, but she doesn’t want to give up her six-figure job to go full-time into a profession in which the lucrative benefits package doesn’t come into place for at least 20 years. The second? That she would do it on a contract basis, focusing on just business law electives, once she reaches her fifties and the kids are out of college. In fact, she would do it for just a small annual sum and without any need for either retirement benefits or healthcare coverage. Third: That her parents, both in their sixties, comfortably retired and still looking for new challenges, would love to teach kids and would do so on a contract basis themselves. Her father, a former school principal who plays in his own band, could definitely teach music as he did when he first came into education five decades ago; while her mother, a former chief nurse practitioner, could definitely take on such electives as health and sex education the same way she has been teaching young girls (including at the local church) for years.

Then she wonders: Why don’t districts just contract with these aspiring teachers? The kids could get high-quality learning in these electives from subject-matter experts who care about kids. Even better, school districts can get this expertise and save millions annually spent on salaries and benefits for teachers working on electives that contribute to student learning, but whose value can’t really be measured (because there are no tests for these areas), and, to be honest, the teachers are not exactly experts with up-to-date knowledge. Why not hire professional musicians as contract music instructors working for several local schools in a district? Or contracting with an auto body shop to teach students about the ins and outs of modern automobiles?

This young corporate lawyer has stumbled onto one of the realities that school reformers and education traditionalists will eventually have to confront: That current- and long-term fiscal realities, along with the need to provide our children with high-quality teachers in core subjects, makes it untenable to keep many of the majority of teachers dedicated solely to elective courses and subjects that may not be at the heart of improving student learning. The fact that many of these teachers aren’t exactly subject-matter experts or have knowledge that is out of date also means that students aren’t getting what the learning they deserve while taxpayers are bearing fiscal burdens that may not make sense. So it is time to develop new solutions that will help our kids get enriched learning experiences while also saving money. In many cases, this may mean replacing full-time teachers in elective courses with contractors and part-timers from the millions of aspiring teachers of middle age who already have the subject-matter competency and experience with children to do the job.

President Barack Obama played up the prospect of teacher layoffs earlier this month as part of his efforts to pass his $450 billion American Jobs Act stimulus plan, 30 percent of which is slated toward supposedly keeping teachers in classrooms. The fact that districts do as much as they can to avoid teacher layoffs, along with the ineffectiveness of Obama’s previous teachers’ union bailout plans, and the estimated 24,000 teachers that will be added to payrolls (according to U.S. Department of Education estimates) means that few teachers will lose their jobs in the next year.

But fewer teachers will be kept in classrooms over the next decade. Why? Start with the $137 billion in state budget shortfalls over the next two fiscal years. After years of increasing education spending, states are now reducing their subsidies, forcing districts to pare their own budgets. Districts have been able to find cuts in other areas (including trimming custodial staffs) and even hold off on raises. But eventually there will be teacher layoffs.

Then there are the long-term issues. With $1.4 trillion in teachers’ pension deficits and unfunded retiree healthcare costs, states can no longer afford to simply increase the number of teachers. The fact that fringe benefits have increased from 28 cents for every dollar of teacher salary to 32 cents is proving costly to districts. Moving away from defined-benefit pensions is one key step toward reducing these burdens, as will require teachers to contribute more to their benefits. But it won’t be enough. Headcounts will have to be cut.

If 1.6 million Baby Boomer teachers actually retire, as Denise Forte of the U.S. Department of Education predicts, then that will make some of those headcount decisions easy. Districts will simply have to whittle down by attrition, hiring fewer teachers to replace those heading into retirement. But given the personal financial difficulties — from mortgages under water to college bills for their kids — that some teachers in that age range could be facing, don’t count on it. And given that previous claims of mass retirements have not come to fruition, no one can count on attrition alone.

Then there is the most-important reason why we need fewer teachers: There are far too many laggards in our classrooms who are poorly-serving our kids. While middle-class families and teachers’ unions have been fans of class size reduction efforts that have led to more teachers working in classrooms with fewer kids, the initiatives have proven to be ineffective in improving student achievement. If anything, the addition of more teachers may actually dilute quality because ed schools — which were doing a poor job of training teachers before the advent of class size reductions — are sacrificing quality for quantity, doing an even worse job of weeding out the chaff from the wheat. Kids may be better off with larger classes taught by high-quality teachers.

There will be layoffs. The question is what this will look like. Elementary school teachers, who make up 1.7 million of our teachers, will likely be safe. As I discussed earlier this month, there could likely be more specialization, which means there will be just as many elementary school teachers working in the next decade as there are now. More importantly, a high-quality elementary education will ensure that kids will make it through the middle school years and high school toward graduation. Cutting elementary school teachers doesn’t make sense.

As for those working in the middle and high school ranks? A different story. If laws requiring reverse-seniority (or last in-first out) layoffs are reversed in the coming years, then districts can eliminate costly laggard teachers in reading, math, science and history regardless of their experience. Thanks to more-rigorous teacher evaluations coming into place such as the IMPACT system in D.C., this work becomes easier for districts to do. But given that the core courses (along with foreign languages and special education) account for only 33 percent of the 1.1 million teachers working in our nation’s high schools (and likely, a similar percentage of middle-school teachers), the teachers working in subjects that are either considered electives or non-core subjects such as music will also face the axe.

One could just make subject every school course to testing. But that won’t fly with many parents or even some school reformers. Why? Some believe that subjecting these courses to tests would ruin the enriching experiences that students may gain from them; while they are willing to subject students and teachers in core subjects to testing, they think the music teacher, the shop class instructor, and the art teacher should not have to deal with that stuff. Then there is the cost of testing those subjects themselves, which may be prohibitive financially and politically compared to the gains that can be reaped. Certainly there should be testing for foreign language proficiency; this makes sense in an age in which learning Mandarin or Spanish can be critical to lifelong success in an increasingly global economy. But one can imagine the cultural and political debates over what should be covered in a music appreciation exam.

What cannot be measured will not matter, or at least, not matter enough to employ a full-time teacher to hold that job. Since tests won’t be administered for these electives, those teachers cannot be evaluated in any meaningful way. Certainly, principals can evaluate for observable aspects of teaching, but not for the most-important and unobservable matter of student achievement. More importantly, since outcomes can be measured, American public education will be required to rely on outputs such as teacher credentials that do not correlate with student achievement. If depending solely on credentialing doesn’t make sense for measuring the performance of teachers in core subjects, it won’t make sense for those in electives either.

This leads to a predictable result: Fewer teachers in health, music, art, and other subjects. And it should. The salary and benefits are too costly. But this doesn’t have to mean the end of electives. After all, music and art are critical in building the background knowledge children need to be fully literate. One can also justify the existence of health and sex education courses. Then there are the vocational courses, which have, for most of the past 80 years, been way stations for students that American public education deemed incapable of college preparatory learning. The reality that blue-collar workers need the same high-level reading, math and science skills that white-collar counterparts must have makes vocational ed less necessary. But it is a good thing for kids to learn about woodworking; it can offer an outlet for kids for self-expression as well as learn a skill they can use at any point in life (think about having to put together a cabinet or fix shelving). Vocational courses can also offer new, relevant ways for kids to learn the college preparatory math and science lessons that they are being taught in traditional classrooms.

But this doesn’t mean continuing to keep hundreds of thousands of teachers in electives on full-time payrolls. One possibility starts with the millions of middle-aged professionals — including lawyers, nurses, blue-collar welders, auto shop owners and professional musicians — who are ready, willing and able to take on teaching those subjects at least on a part-time or contractual basis. One can imagine a district putting together a team of professional musicians who can teach at several schools throughout the school year, or even working with a technical university to provide weekly shop electives to interested students. I can easily imagine my mother-in-law, a social worker who now sits on Arkansas’ minority health commission, teaching health classes at a local high school — or my own mother teaching information technology classes to high schoolers in the Atlanta suburb in which she lives.

Best of all, these mid-career and Baby Boomer professionals, many of whom already demonstrated experience and have their retirement benefits already squared away, won’t need pensions, 401-K plans, or even much in the way of salary. And as Martin Haberman has noted, teachers coming into the profession late in life also have the practical skills needed to manage classrooms, command the respect of students, and get their job done with little supervision.

This not only creates an opportunity for schools (in terms of high-quality instruction at a cost savings) and students (who get relevant, up-to-date instruction with real professionals in those fields), but even for ed schools and alternative certification groups who can offer short courses on teaching method, cultural competency and other aspects of teaching. And it doesn’t need to take four years to get the needed certification. One can imagine a year-long clinical-based teacher training that gets aspiring teachers into the field within three months of passing tests that show subject competency, entrepreneurial drive and caring for children.

Education traditionalists, of course, don’t want to have this conversation because it means rethinking what a teaching career should look like. For the National Education Association and the American Federation of Teachers, in particular, it also means fewer members upon which they can count for dues that they use to maintain their declining influence. As for school reformers? Far too many have been happy with talk about stretching spending and wringing out needed efficiencies in aspects of education such as transportation and building maintenance. They have also pressed admirably to end the array of practices — from reverse-seniority layoffs to abysmal performance management — that has been one of the causes of the nation’s education crisis. But with teacher salaries and benefits account for 60 percent of current spending, questions about teacher staffing can no longer be bypassed. We owe it to our children and to teachers to honestly think through what staffing can and should look like in the coming decades.

The reality is that there will be fewer teachers in America’s classrooms. Now is the time to discuss what that will look like and how we can ease the transitions that are going to come.