How does the structure of U.S. teacher unions compare with that of other developed countries? What does this structure imply for the performance and flexibility of our schools? A comparative survey shows U.S. teacher unions just two major ones form an unusually concentrated oligopoly:

European countries tend to enjoy four or more teacher unions, representing a variety of ideologies, teaching methods, and religious orientations.

Some countries restrict political action by public sector unions, or have teacher choice systems for dues, or parental choice systems for schools, that encourage diversity and diffusion among teachers unions.

Some Asian countries have low membership rates of 40% or less, or outlaw true teacher "unionism" altogether. Examples include Singapore, Taiwan, and Korea.

Do these differences matter? While the data in this limited survey do not support sweeping conclusions, some fairly strong correlations emerge from the data:

• Countries with low "union concentration" whether because of diverse union choices, limits on union political activity, or low union membership altogether perform better on standardized reading, math, and science tests.
• Countries with union oligopoly structures where a small number of ideologically and operationally homogenous unions wield great political power tend to have more rigid school systems that resist reform.

Policies that would actually increase union concentration, like a proposed merger of America's two major teacher unions, would hurt performance and reduce flexibility.

Policies that would lower the barriers to entry for new teacher associations might provide a healthy degree of competition and diversity to U.S. education. They would tend to make the system more responsive to parents and to institutional reform.