SANTA ANA, Calif. -- A technology-driven teaching method known as "flipped learning" because it flips the time-honored model of classroom lecture and exercises for homework is catching on in schools nationwide as a younger, more tech-savvy generation of teachers is moving into classrooms.In "flipped learning," the lecture becomes the homework and class time is for practice."It was hard to get used to," said 11th-grader Timmy Nguyen, whose pre-calculus teacher in Santa Ana has "flipped.""But then I stopped complaining and I learned the material quicker. My grade went from a D to an A."Although the number of "flipped" teachers is hard to ascertain, the online community Flipped Learning Network now has 10,000 members, up from 2,500 a year ago, Executive Director Kari Afstrom said.Under the model, teachers make eight- to 10-minute videos of their lessons using laptops, often simply filming the whiteboard as the teacher makes notations and recording their voice as they explain the concept.The videos are uploaded onto a teacher or school website, or even YouTube, where they can be accessed by students on computers or smartphones as homework.Class time is then devoted to practical applications of the lesson.The concept emerged five years ago when a pair of Colorado high school teachers started videotaping their chemistry classes for absent students."We found it was really valuable and pushed us to ask what the students needed us for," said one of the teachers, Aaron Sams, now a consultant who is developing on online education program in Pittsburgh. "They didn't need us for content dissemination; they needed us to dig deeper."He and colleague Jonathan Bergmann began condensing classroom lectures to short videos and assigning them as homework."The first year, I was able to double the number of labs my students were doing," Sams said. "That's every science teacher's dream."Although the method has been more popular in high schools, it's now catching on in ele-mentary schools, Afstrom said.