In school districts where YouTube is blocked, teachers sometimes go to great lengths to show videos that they believe enhance their lessons.

“It can be a challenge,” said Jesse Spevack, assistant principal at the NYC iSchool in the TriBeCa neighborhood of Manhattan, which limits students’ ability to navigate and post on the Web from computers in classrooms and labs. “I’ve tried opening the window and loading the video on a laptop, or bringing a video in on my phone — or just asking the kids in my class, because there’s always some proxy hack site that a student will know how to use.”

When those techniques fail, he puts links to lessons on Khan Academy, TED talk videos and HipHughesHistory, a set of history-related videos created by a history teacher in Buffalo, on the class Web site, and asks students to view them outside of school.

Mr. Spevack said he understands New York City’s policy. “There is a lot of stuff on YouTube I wouldn’t be comfortable with my students seeing,” he said, “so I think trying to set up a way to differentiate content that is useful to schools and teachers from everything else is an awesome idea.”

Teachers have proved to be Google’s best emissaries for the filtering system, said Angela Lin, head of YouTube EDU. “The challenge now is getting these enthusiastic individual teachers to work with administrators and I.T. staff to make this a reality.”

Google has begun to create and solicit new channels in the hope of increasing its appeal. For instance, TED, a nonprofit group that works to spread the ideas of thought leaders from around the world, on Monday will start a channel that will eventually have hundreds of videos as part of a new educational initiative.

Brady Haran, the producer of the Deep Sky astronomy videos and Numberphile math videos, will develop two of the channels. “I don’t really think of them as lessons or teaching,” he said of his videos. “It’s far more useful to show something that’s tangential to the lesson, but supports it.”