I disagree with some progressive presidential candidates on free public college education for everyone. While it sounds enticing, I think it is misdirected. It all comes down to economics.

Start at the beginning, in pre-school. Pre-school is especially important for low-income students, and studies show that it can be very effective in preparing all children for subsequent education.

Next, consider primary and secondary education. As you know, a large share of funding for public K-12 education comes from the local property tax. There are two problems with this.

• First, the property tax is highly regressive, meaning that the burden of the tax falls primarily on lower income people. Economists define "tax burden" in terms of the percent of a family's income paid on the tax. Even though lower income families generally pay a smaller amount of money on the property tax, they pay a larger percent of their income on the tax than do higher income people. This is because lower income people spend a much larger percent of their income on their homes, including rentals. (High-income people may have much nicer and more expensive homes, but they spend a larger percent of their income on savings and financial investments and a smaller percent of their income on their homes.)

• However, the main problem with property tax funding is that it creates inequality in education. Children fortunate enough to live in high income/high property-value school districts attend well-funded and high-quality K-12 education. Those who come from lower property-value districts attend schools that are inadequately funded. Unless there is some "equalizing formula" that adds state and/or federal dollars to less well-funded schools, the quality of the education for low-income kids is questionable.

Children in lower-funded schools may fare more poorly in primary education. As a result, they may be unprepared for high school and their high schools may be of poor quality. These all can result in higher high school drop-out rates, or grades too low to get students into and/or succeed in college.

For these reasons, poor students are less likely to attend and/or succeed in college.

There is, of course, a racial dimension to this, just as there is a racial dimension to poverty. Thirty-five% of non-Hispanic white people obtain a bachelor's degree or higher. This rate is only 23% for African Americas, and just 6% for Hispanics. High school dropout rates are 4.6% for whites, 6.5% for African Americans and 9.2% for Hispanics.

And, there is a global dimension. Poor education for many U.S. students brings down our global comparisons. For example, the average primary education pupil to teacher ratio is often used as a measure of quality. The U.S. pupil to teacher ratio is 23, which is the highest (worst) among the top 15 Western industrialized countries. Poorer countries, such as Cuba, have a better ratio than us.

There is another important, though almost entirely overlooked, problem for low income college students. They may receive financial assistance, but still face prohibitive opportunity costs. Economists define opportunity costs as "what is given up in order to receive something else." These opportunity costs include any full-time wages given up while attending college. Lower-income students and their families simply cannot afford these opportunity costs, even if their tuition and room and board is free.

Some of these problems can be overcome with appropriate policies, including:

• Adequately fund Head Start programs for poor, pre-K children.

• Supplement property taxes with state and federal "equalizing funds" that improve funding in low income school districts to equalize with those in higher income school districts. Some states do this.

• Expand Pell Grants to reduce or eliminate tuition for low income students in traditional public universities, as well as those in technical, community and two-year colleges. Provide funds for living and other expenses for these students and provide additional assistance to overcome their opportunity costs. Provide remedial education for those students less prepared for college.

The problem with "free public college education for all" is that some college students have less need for government subsidies. The dollars could be better spent for low- and middle-income students.

All this extends to another progressive policy proposal: the elimination of student debt. It's true that many students graduate (or don't graduate) from college with staggering student loans. And, not all college graduates go on to high-salary jobs. For this reason, we should target loan forgiveness to graduates earning relatively lower incomes, including those who were unable to graduate.

We as a nation do not necessarily believe in income equality, but we do believe in equal opportunity. This begins with equal opportunity for a quality education. But just believing in this doesn't make it so. Well-thought out policies do.