These four teens from Brattleboro, Vermont were most likely cadets, maybe in a marching band?
Photographer Caleb Howe chose to take this picture horizontally, preferring to catch the boys in close-up. One of them is smiling and the others seem comfortable in front of the camera.
The card has yellowed with the passing of time.

Caleb Howe & Son. Back of card.
Photographer: Caleb Lysander Howe & Son (John C. Howe). Brattleboro. Vermont.
Caleb Lysander Howe (1811-1895) was a highly respected photographer in his home state of Vermont. He began his craft on the road in the late 1840s. During the Civil War he photographed a great number of soldiers who queued at his studio door for a chance to get their portrait taken. He also photographed Union General John W. Phelps on a card with the similar backing.
Howe’s son joined him in the business in the early 1880s. Since his initials appear on that cabinet card as well as the one I have I believe these were made a couple of decades after the war, by the end of the general’s life who passed in 1885.
Caleb Howe was also a singer and musician. There is a page dedicated to his life that is worth a look. There you can see the John W Phelps card.