Mrs. Meade and the Schoolboy Prank: A Short Story. The Mrs. Meade Mysteries, #5.2

"I do believe in coincidences, surely, " said Mrs. Meade, "but when they coincide with perfect alibis and impossible thefts I tend to doubt them."When the Wellmans receive a letter from their son's boarding-school informing them that Allen has been accused of stealing from a classmate, they promptly head for Denver to investigate. The situation looks bad, since almost the whole rest of the school have perfect alibis.
It's fortunate that Mrs. Wellman thought to bring along her friend Mrs. Meade to see if she can spot the solution... This stand-alone short story can be enjoyed in any order with the rest of the Mrs. Meade Mysteries, but does feature characters introduced in Book 5, The American Pony.