WASHINGTON (AP) --American teachers must do more to help students understand the concepts of math, not just the mechanics of how to solve an algebra or geometry problem, an international review of 8th-grade classes suggests.

The four-year study analyzed videos of teaching techniques in seven countries, including six that score higher than the United States in math achievement: Japan, Hong Kong, the Czech Republic, Switzerland, the Netherlands and Australia.

Researchers cautioned Wednesday they cannot draw direct links between the teaching techniques and the countries' levels of success, particularly because so many factors affect learning. They also said the study did not aim to pinpoint features of good teaching, although more review is planned that could help produce specific tips for U.S. teachers.

The authors said U.S. teachers spend less time than counterparts in higher-achieving countries on explaining math's underpinnings.

"They're more focused on getting the answers, and less focused on giving students the opportunities to really engage in serious mathematical work," said James Stigler, chief executive officer of LessonLab, which conducted the study for the Department of Education.

"Finding ways to engage students in conceptual thinking -- it doesn't fit within our cultural script of how you teach a math class," he said.

How those specific skills are developed "may be the real key," said University of Delaware professor James Hiebert, another leader of the math video study. Even when they present problems that link ideas to formulas, U.S. teachers often end up in step-by-step mode.

"We have to worry about whether students are understanding what they're being asked to do," he said. For example: "Why is that skill working? Why do you divide now? Why do you take the square root here? Why am I finding the lengths of the these two diagonals?

The study underscores there is no single correct way to teach math, officials said.

"It shows there are many paths to excellence in teaching," said William Frascella, an education leader of the National Science Foundation, a partner in the study. "Unfortunately, it appears from initial results that the United States is not able to use any one of these paths in a consistent and sustained manner."

The Education Department plans to make available public copies of videotape examples in compact disc form. Results of the science-video portion of the Trends in International Mathematics and Science Study will be released later.