My son's school does it much as Fungo describes. Each semester, students take 8 classes and they are staggered, with 4 classes on "A" days and 4 classes on "B" days. A typical 2-week period will look like this:
Week 1 - Mon (A); Tues (B); Wed (A); Thurs (B); Fri (A)
Week 2 - Mon (B); Tues (A); Wed (B); Thurs (A); Fri (B)
Each class lasts 1 1/2 hours. If you're taking a 1-year course such as English or geometry, you take it all year. Other courses, such as government or speech, last only 1 semester.
Anyone in music (band/orchestra/choir) or athletics (all sports) takes that class for one period of every day, so in effect they are taking 6 academic classes and 2 activities classes. For my son, that means attending academic classes plus a 30-minute lunch from 9 a.m. to 2:30 p.m. and baseball class from 2:30-4 p.m. each day. As you can imagine, he loves it!
This past year, my son transferred from a private school to this public school. My son's private school team was a very good one, making it to the state tournament in May 2006, but we have seen a vast difference in the quality of training plus emphasis on the sport at his public school. At the private school, there was no athletic class for baseball and players were on their own for conditioning. At the public school, there is athletic class year-round, where the coach is able to focus on weight-training, speed training, drills, scrimmages, etc. Actual baseball practice begins in late January and occurs from 4 to around 6 or 6:30 p.m. Monday through Friday. The varsity baseball team has at least 4 members who also play football. They have football class the first class of each day and are not enrolled in baseball class, but they get their conditioning in football.
Many, many schools in Texas structure their school days and practices this way. Perhaps this is one of the reasons there are so many good baseball players in Texas! Academically, as long as the players take several AP or honors classes, they do absolutely fine in college. My son's school has an extremely competitive atmosphere not only on the field, but also in the classroom, with high-achieving students who are spurred on by their high-achieving parents.