Lego is looking to keep its plastic bricks out of the trash. The Danish toymaker is testing a way for customers to ship their unwanted bricks back and get them into the hands of other kids. It said yesterday that customers in the U.S. can print out a mailing label on its site, dump their used Lego bricks in a box and ship them off for free. Lego said the pieces will be cleaned, put in a box and given to Teach for America, a nonprofit that will donate them to classrooms across the United States. Some bricks will be also sent to the Boys & Girls Clubs of Boston for their after-school programs. Lego said if the test is successful, it may expand the program beyond the U.S. next year. The company typically tells its customers to keep their bricks or pass them on to others. But some have asked for another way to donate them, said Tim Brooks, Lego’s vice president of environmental responsibility.