Taken to the woodshed
Taking someone to the woodshed means meting out punishment in private, out of the view of any onlookers.
The phrase dates from an era prior to the early years of the 20th century, when (a) most people lived in rural areas, (b) people had woodsheds behind their houses for the storage of firewood, and (c) corporal punishment was commonplace. It typically referred to the father taking a child out back, either into the woodshed or behind it, for a thrashing. The reasoning was ostensibly to spare the mother having to listen to the child's wailing.
In the modern era, that sort of thing rarely happens, but many people find that, for various reasons, chastisement, reproof, reprimands, and punishments, are best done away from other people's prying eyes and ears. So people are described as being "taken out to the woodshed".
There is another use of the term, in music, to refer to extremely intense practice of a troublesome spot in a piece, presumably because it is so intense that it might be annoying if heard by other people. So a band leader might say "Woodshed the section at measure 55, and we'll try it again next week."