President Barack Obama has high praise for science projects from some high-achieving students, telling them, "this stuff is really cool."

Obama is speaking at a White House , an event the president says is one of his favorites. Monday's event marked the third White House science fair and highlighted projects by student winners of science, technology, engineering and math competitions.

About 30 student teams were invited to show their projects. Rockets and robots are among the exhibits, as well as a fully functioning prosthetic arm made mostly with parts generated using a 3-D printer.

The president says the students make him hopeful about the nation's future.

Obama also announced a new national service effort to link AmeriCorps members with that promote science, technology, engineering and math.