When students don't show up for class, they tend to learn less. No surprise there. That's why school districts and social service agencies develop programs to improve student attendance and reduce truancy.

Turns out that teacher attendance matters, too. The more time teachers spend away from their classrooms, the more student achievement suffers, according to recent studies. That means school officials and educators should take steps to reduce teacher absences and use substitutes more effectively.

This is not just about the inevitable times when Mrs. Jones is out a day or two with the flu. Nationwide, school officials reported that the number of subs needed to fill regular teaching vacancies doubled between 1994 and 2004. Federal Education Department data shows that about 20 percent of public schools use substitutes to fill longer-term openings, often in subject areas where there are teacher shortages. And that makes it more likely substitutes will be asked to teach outside their areas of expertise.

Studies from the University of Washington and Duke University indicate that districts rely so heavily on temporary teachers that American students spend the equivalent of a full year with a sub in 12 years of schooling. Even as few as 10 days with a replacement teacher, according to the study, can lower student test scores.

In Minnesota's three largest districts, regular teachers miss tens of thousand of days a year. Anoka-Hennepin educators were out of the classroom 37,702 days in 2006-07, with more than 14,000 of those days spent in training or meetings, the district told the Star Tribune recently. St. Paul and Minneapolis schools also reported that roughly a third of missed teacher days were for staff development.

Training and consulting with colleagues is important; teachers need continuing education for their jobs just like other professionals. However, given the impact on students, districts and educators should look for creative ways to offer training and minimize classroom absences. St. Paul, for example, is doing more on-the-job training. Coaches observe teachers with their students and provide feedback. Using that kind of training, the district has cut by half the number of days teachers are away in meetings.

Understandably, teacher absences cannot be eliminated. Teachers get sick and need personal time off. They may be even more prone to illness like colds and flu, given their close contact with children. Those situations cannot be controlled by districts and educators. But they can make changes on the staff development front, similar to those used in St. Paul. District leaders can also examine ways to provide financial or other incentives to reduce the amount of sick and personal time taken.

Another way to address the problem is to prepare for times when substitutes are needed. Some teachers do an excellent job of planning, providing detailed lesson plans to assure that students don't miss a beat. That kind of preparation should be more widely practiced.

Reducing teacher absences alone is not the answer to all education woes. But giving teachers and pupils more time together is one of several factors that can improve student achievement.