A common story line in American education policy is that public school teachers are underpaid—"desperately underpaid," according to Education Secretary Arne Duncan in a recent speech. As former first lady Laura Bush put it: "Salaries are too low. We all know that. We need to figure out a way to pay teachers more."

Good teachers are crucial to a strong economy and a healthy civil society, and they should be paid at a level commensurate with their skills. But the evidence shows that public school teachers' total compensation amounts to roughly $1.50 for every $1 that their skills could garner in a private sector job.

How could that be? First, consider salaries. Public school teachers do receive salaries 19.3% lower than similarly-educated private workers, according to our analysis of Census Bureau data. However, a majority of public school teachers were education majors in college, and more than two in three received their highest degree (typically a master's) in an education-related field. A salary comparison that controls only for years spent in school makes no distinction between degrees in education and those in biology, mathematics, history or other demanding fields.

Education is widely regarded by researchers and college students alike as one of the easiest fields of study, and one that features substantially higher average grades than most other college majors. On objective tests of cognitive ability such as the SAT, ACT, GRE (Graduate Record Examination) and Armed Forces Qualification Test, teachers score only around the 40th percentile of college graduates. If we compare teachers and non-teachers with similar AFQT scores, the teacher salary penalty disappears.

While salaries are about even, fringe benefits push teacher compensation well ahead of comparable employees in the private economy. The trouble is that many of these benefits are hidden, meaning that lawmakers, taxpayers and even teachers themselves are sometimes unaware of them.

Data on employee benefits from the Bureau of Labor Statistics (BLS), for example, do not include retiree health coverage, which for teachers is worth about an additional 10% of their salaries. Because of differing accounting rules between the public and private sectors, BLS data also make teachers' defined-benefit pensions appear only slightly more generous than the typical 401(k) plan found in the private sector.

In reality, a teacher who retired after 30 years of service with an annual salary of $40,000 might receive guaranteed annual pension benefits of about $20,330. Under a typical private 401(k) plan, a guaranteed annual benefit might be only around $4,450 (assuming the money is invested in U.S. Treasurys and the employee buys an annuity).

BLS data on paid leave for teachers count vacation days only during the school year, omitting summer and long holiday breaks. A valid pay comparison should include this extra time off, in which teachers can enjoy longer vacations or earn additional income.

Properly counted, a typical public school teacher with a salary of $51,000 would receive another $51,480 in present or future fringe benefits. A worker in private business with the same salary would receive around $22,185 in fringe benefits.

Finally, despite recent layoffs, teachers still have greater job security than workers in private businesses. While employment in education declined by 2.9% between September 2008 and July 2011, according to BLS data, overall private-sector employment declined by 4.4%. Moreover, from 2005 through 2010 the unemployment rate for public school teachers averaged 2.1%, versus 4.1% for private school teachers and 3.8% for occupations that some consider comparable, such as computer programmers and insurance underwriters.

Job security protects against the loss of compensation suffered by the unemployed, and it also protects a position in which total wages and benefits are on average above market levels. This job security is surely valuable.

Consider that one-fifth of the highest-performing public school teachers in Washington, D.C., recently declined to give up even part of their job security in exchange for base salary increases of up to $20,000. According to our model—which factors in the probability of becoming unemployed, the average duration of unemployment, the level of unemployment insurance benefits, and the risk aversion of public employees—job security is worth about an estimated extra 9% of compensation.

One important caveat: Our research is in terms of averages. The best public school teachers—especially those teaching difficult subjects such as math and science—may well be underpaid compared to counterparts in the private sector.

Nevertheless, most public school teachers would not earn more in private employment. According to our analysis of the Census Bureau's Survey of Income and Program Participation, the average person who moves into teaching receives a pay increase of almost 9%, while the average teacher who leaves for the private economy must take a pay cut of over 3%.

This is the opposite of what we would expect if teachers were underpaid. It also helps explain why more people seek teaching jobs—as measured through the number of teaching graduates and applications for teaching positions—than can possibly find them.

In short, combining salaries, fringe benefits and job security, we have calculated that public school teachers receive around 52% more in average compensation than they could earn in the private sector.

The compensation premium is especially relevant today, as states and localities struggle with budget deficits. Restraining the growth of teacher compensation—in particular, pension and retiree health benefits that outstrip what comparable private-sector workers receive—could help balance budgets and perhaps restore school resources lost to rising labor costs. Broader pay reform should give school administrators greater flexibility to reward the best or most-needed teachers with high salaries and benefits, while encouraging the least effective ones to improve or to leave the profession.

Effective reform, however, requires knowing all the facts about teacher pay. Policy makers and the public should not accept at face value that the typical teacher earns far less than he or she would in the private sector. The evidence points to a very different conclusion.

Mr. Biggs, a resident scholar at the American Enterprise Institute, and Mr. Richwine, a senior policy analyst at the Heritage Foundation are authors of the new paper, "Assessing the Compensation of Public School Teachers" .