But block scheduling still has its enthusiastic supporters. The idea was made popular in recent decades by school reformers, who questioned the almost universally accepted tradition, in place since the early 1900s, of requiring all high school classes to meet for 45 to 50 minutes every school day.
Lengthening class periods, they recommended, would force teachers out of a lecture-only mode of teaching, allow students to engage more deeply in material, and cut down on disciplinary problems and time wasted in the hall between classes. The idea gained momentum rapidly throughout the 1990s and got a significant boost in 1994, when the National Education Commission released its "Prisoners of Time" report, which included a recommendation that high schools experiment with block scheduling.
Between 25 and 40 percent of high schools now use block scheduling, according to some estimates. In some states, that figure is significantly higher. In North Carolina, for instance, almost 90 percent of high schools have embraced the system. Some middle schools across the country have also moved toward the longer class periods.
There are two basic models for block scheduling. One, known as the 4 x 4, requires students to take four lengthy classes a day for a semester. The next semester, they move on to four different subjects.
The other model is sometimes called an A-B-A-B, or alternating system. Students have four extended class periods a day, but then alternate with four different classes the next day, allowing them to take eight classes spread out over the course of the school year.