By Karen Gutierrez
The Cincinnati Enquirer

Worried about sleep deprivation among teenagers, the Minneapolis Public School District changed its high-school start times in 1997.

Afterward, students reported less sleepiness and better moods. But the impact on performance hasn't been as clear, even though the district's experience is cited as evidence that later times are best.

About 12,000 Minneapolis students were affected when the large, urban district went from a start time of 7:15 a.m. to 8:40 a.m. for its seven high schools.

The effect was studied extensively by researchers at the University of Minnesota.

Among their findings:

• After the change, attendance improved for students who had unstable enrollment, meaning they had switched schools in a two-year period. For example, ninth-graders in this category had an attendance rate of 72 percent before the change and 75 percent after.

Attendance did not significantly improve for students with at least two years of continuous enrollment. Their rate continued to hover around 95 percent.

• After the change, students were more likely to remain in the same high school as opposed to moving among schools or districts. For instance, in 1995,54 percent of sophomores had been in the same school for two years in a row, compared with 66 percent in 1999.

• After the change, students reported getting an average of seven hours and 59 minutes of sleep each night. This compares with the seven hours and 1 minute reported by students in a similar district with a 7:30 a.m. start.

• Students in schools with an 8:40 a.m. start reported less depression and sleepiness than those in the comparison school.

• In a survey of 335 teachers, 57 percent said more students were alert during the first two periods after the start time changed.

• Student grades did not appear to significantly improve. But the researchers lacked confidence in this finding, saying it proved nearly impossible to track grades earned by thousands of students over time.

The entire report can be found at Web site

E-mail kgutierrez@enquirer.com