Clarence Young was a house pseudonym

Pseudonym

A pseudonym is a name that a person assumes for a particular purpose and that differs from his or her original orthonym...

 used by the Stratemeyer Syndicate

Stratemeyer Syndicate

The Stratemeyer Syndicate was the producer of a number of mystery series for children, including Nancy Drew, the Hardy Boys, the various Tom Swift series, the Bobbsey Twins, the Rover Boys, and others.- History :...

 for series of books for boys, the most well-known being the "Motor Boys" series.

The following series were published under the name Clarence Young:

• Jack Ranger—6 volumes (1907–1911)
• Motor Boys
  Motor Boys
  The Motor Boys were the heroes of a popular series of adventure books for boys at the turn of the 20th century issued by the Stratemeyer Syndicate under the pseudonym of Clarence Young. This series was published by Cupples & Leon and was issued with dustjackets and glossy frontispiece...
  
  --22 volumes (1906–1924)--The first ten were illustrated by Charles Nuttall
  Charles Nuttall
  Charles Nuttall was an Australian artist noted for his illustrations.Nuttall, son of James Charles Nuttall, was born at Fitzroy, Victoria. He received his art training at the national gallery, Melbourne, and became a contributor of drawings to the Bulletin, Life, and other journals...
  
  --Volumes 1, 2, and 8 ghostwritten by Howard R. Garis
• Racer Boys—6 volumes (1912–1914)

The pseudonym "Clarence Young" was also used by Edward Stratemeyer

Edward Stratemeyer

Edward Stratemeyer was an American publisher and writer of books for children.He is one of the most prolific writers in the world, producing in excess of 1300 books himself, selling in excess of 500 million copies, and created the well-known fictional book series for juveniles including The Rover...

for a few football stories published in turn of the century boys magazines.