Sibko is a Clan compound word for "sibling company," the primary means by which Clan warriors are raised and trained. Sibkos are generally collections of trueborn children produced by the same geneparents and number upwards of one hundred children. Some Clans will stock an entire sibko from offspring of a prestigious Bloodname or from a particular Bloodheritage, though in many offspring of several different Bloodnames are common. Clan Wolf in particular is known for creating sibkos from a number of different Bloodnames and subcastes, and while such units tend to number only twenty, greater emphasis is placed on cooperation.
Trueborn children will be placed in a sibko after having survived training in a Crèche. Here they begin training in skills necessary for their individual role, whether as MechWarriors, aerospace pilots or Elementals, until around their 20th birthday when they either pass their Trial of Position and become a full warrior, or fail.
Each warrior type is trained separately to keep competition fierce yet balanced, and judging a cadet's worth begins early in their career, though the weeding-out process generally doesn't begin until they reach maturity. Each cadet is tested for intelligence, command ability, reflexes and strength, and above all martial skills, all while being indoctrinated in Clan history and philosophy. The severity of this testing depends on the individual Clan's policy: stricter testing guidelines during this period means fewer warriors though theoretically of a higher quality, while others may conduct sibko life under less stringent rules yet use a more difficult Trial of Position to ensure high-quality cadets enter front-line units.
Regardless of the measures used by the end as few as four or five cadets will pass their initial Trial of Position and graduate to full-fledged warriors. Those who fail this final test are relegated to the civilian castes, though some progressive Clans do allow a secondary Trial of Position to allow potential warriors the chance to rank in a second-line unit.
Freeborns who have proven themselves fit for warrior training are also placed into sibkos and undergo a training regime designed to make them the best warriors possible. High casualty and dropout rates from these freeborn sibkos are only compounded by the callousness of the training officers assigned to them, as happy to see these cadets dead as pass their Trial of Position.
- Clan Jade Falcon calls their Sibko instructors Falconers.
- Clan Sea Fox, by the 32nd Century, refers to their Sibkos as Shivs and their instructors as Shiv-trainers.
- Clan Hell's Horses call their Sibko instructors Wranglers. 
- Field Manual: Warden Clans, p. 18
- Field Manual: Warden Clans, p. 170
- Field Manual: Crusader Clans, p. 17
- Field Manual: Crusader Clans, p. 162
- Classic BattleTech RPG, p. 39
- Classic BattleTech RPG, p. 201
- Classic BattleTech RPG, p. 37
- Way of the Clans
- Hunters of the Deep, p. 14, 34
- A Living Epitaph, p. 2