This is a set of 5/6 of  "The Racer Boys" series by Clarence Young (a Stratemeyer syndicate house name)  the author of the Motor Boys series. It was published by Cupples & Leon in New York in 1912-13. The books tell the adventures of the Racer boys in the early 1900s. 

These books are hard to find but are not in great condition.  All are complete as far as I can tell.  Please see below and pictures for further information on  condition.

The Racer Boys, G-, Wear and dirt on cover.  Tear up half the spine.

at Boarding School, G, Wear on cover and one loose page (illustration)

to the Rescue, G, wear on cover.

on the Prairies, G, wear on cover with red stain between cover and spine.

on Guard, Poor +, Damage at bottom of front cover and spine. Wear on cover.  All pages readable.