When do Boy Scouts start using patrols and what is the ideal size?

"The patrol system is not one method in which Scouting for boys can be carried on. It is the only method." —Lord Baden-Powell, Scouting's founder

The building block of the troop is the patrol. Patrol sizes may vary but (according the numerous BSA publications) the ideal patrol size is eight Scouts. Although it could range from around 6 to 10 and still be functional; any smaller or bigger and the patrol dynamic changes greatly and doesn’t work.

Types of Patrols

There are three kinds of patrols: new-Scout patrols, regular patrols, and Venture patrols.

	New-Scout patrols are for 11-year-old Scouts who have recently joined the troop and are together for the first year in the troop. An older, experienced Scout often is assigned as a troop guide to help the new-Scout patrol through the challenges of troop membership. An assistant Scoutmaster should also assist the new-Scout patrol to ensure that each Scout has every opportunity to succeed right from the start.
	Regular patrols are made up of Scouts who have completed their First Class requirements. They have been around Scouting long enough to be comfortable with the patrol and troop operation and are well-versed in camping, cooking, and Scouting's other basic skills.
	A Venture patrol is an optional patrol within the troop made up of Scouts age 13 and older. These troop members have the maturity and experience to take part in more challenging high-adventure outings. The Venture patrol elects a patrol leader, who works with an assistant Scoutmaster to put the patrol's plans into action. http://www.scouting.org/scoutsource/BoyScouts/PatrolLeader.aspx