CHICAGO (Reuters) - Playing with blocks helps young children gain language skills, a small study concluded on Monday.

After six months, language scores among half of 175 children aged 1-1/2 to 2-1/2 who were sent plastic blocks were 15 percent higher than a matched group that did not receive the free blocks, according to the study by researchers at the University of Washington in Seattle.

Parents were given ideas about how to help their children play with the blocks, then kept diaries of their children's activities over four days. Finally, all the parents filled out questionnaires that assessed their child's vocabulary, grammar, and other language abilities.

Study author Dimitri Christakis, writing in the Archives of Pediatric and Adolescent Medicine, said unstructured play with blocks stimulates thinking, memory and physical mastery of objects at a time when a child's brain is growing rapidly.

"They are the precursors of thought and language," he wrote of the skills learned from manipulating blocks. "Older children begin to make up stories or scripts for these objects ..."

Such play may also substitute for less stimulating activities such as watching television, he said, adding parents ought to be skeptical of some toy-makers' claims.

"An increasing number of media-based products are making unsubstantiated claims that they can make children smarter, more literate, and more musical," Christakis wrote.

The study was funded by Mega Bloks, owned by Montreal-based toy maker MEGA Brands Inc.