The US college sports system, which generates billions of dollars and draws millions of fans and viewers every year, is a rarity across the globe.

Other nations are puzzled about the concept of student amateurism, and how college students can compete in front of full stadiums and have their jerseys sold, but don't receive a salary. Even in England, where rowing and rugby college events can draw thousands of fans, the competition is more of a friendly match, not an engine for revenue like March Madness or a major college football rivalry.

From their posts across the world, AP reporters described how top athletes are developed in different sports.

Agentina

Players are often signed as children by scouts from local soccer clubs. There is no age limit, although players have to be 18 for Argentine clubs to sell them to foreign teams without parental consent. Parents generally consent to the sale of younger players. Although the player gets a salary, the club gets the transfer fee.

Australia

In Australian rules football and rugby, talented players are scouted in their early teens and join academies and feeder teams run by the big clubs. There are no significant national university-level competitions. Top players get scholarships for elite private high schools, or "centers of excellence" at state government-run schools. Many players take low-paid rookie contracts immediately after high school and use those as the route to the big leagues.

China

The world's most populous nation has an organized state sports system. Children are selected as young as 4 and encouraged to focus on the sport for which they show the most aptitude. They are sent to schools that are sometimes far from their homes. Some of the most successful Chinese athletes have recently broken with the state-controlled system, choosing their own coaches and taking charge of their careers, including tennis star Li Na and young golfer Feng Shanshan.

England

England hasn't won a major title in soccer since the 1966 World Cup and the way talent is developed in the country is often criticized. The best young English players are scouted at an early age by local clubs with trials. The very best often join Premier League clubs' academies before the age of 10. But at big clubs' academies such as Manchester United, Chelsea and Arsenal, English youngsters are competing with foreign talent and very few local players successfully make the transition from youth squad to the club's first team. In 2012, the Football Association opened a national football center designed to emulate its French rivals Clairefontaine. The focus at the football center is to educate coaches capable of nurturing technically gifted players from the age of 5.

India

Young cricket players compete in city and provincial competitions. Schools and universities play a small role in player development. Around the world, the best cricket players represent their countries in youth competitions. The Indian Premier League and the growing popularity of Twenty20 cricket - the shortest form of the game at senior level - is giving more players at a lower level the chance to be professionals, with more clubs, shorter seasons and a chance for players not on the national team to be recognized. The Indian Premier League holds annual player auctions.

Japan

Pro baseball teams can't negotiate with young players until they've finished high school at the age of 18. There is an amateur draft every fall. Heavily scouted teenage players often turn pro straight out of high school, a route that set Yu Darvish and Daisuke Matsuzaka en route to the majors. Other talented players join corporate leagues or go to college to develop their games before signing with professional teams.

Mexico

Mexico's top flight soccer teams are allowed to sign youth players to professional contracts regardless of age. The only restriction is that the length of the contract cannot be for more than three years. Most professional squads have their own soccer schools, where kids from 5 to 12 participate.

Spain

In Spain, young soccer players can sign professional contracts when they turn 16, the minimum work age stipulated by Spanish law. Before that, children join training academies run by soccer clubs that field youth teams in amateur leagues. The most well-known example in Spain is Barcelona's "La Masia" academy, where Lionel Messi started training at the age of 13 when his family emigrated from Argentina. While major clubs may entice the families of some high-profile young talents with offers of jobs or even money, most children play for the training academies of their hometown clubs. Spanish law obliges children to stay in school until 16, the same age when players can join the union.

A similar system exists in Spanish basketball. A player under 16 can play for the club's top team but cannot have a professional contract. This was the rare case for the Minnesota Timberwolves' Ricky Rubio, who debuted for Joventut at the age of 14. Families with children under 16 may receive some type of compensation from clubs in the form of payments to cover travel expenses or to help with their children's studies.

United States

Football and basketball players typically compete in high school, and the best players are scouted by college coaches. Players can attend all-star games and college camps in the offseason. The best athletes sign with colleges for four years, in exchange for a scholarship. The National Football League will not select players until three years after their high school class graduates. The National Basketball Association will not select players until one year after their high school class graduates. College football and men's basketball generate billions in revenue for the schools and the NCAA.

In baseball, players compete in high school and the best are scouted by college coaches and Major League Baseball teams. Some have the opportunity to play in college for full or partial scholarships, or sign professional contracts after high school. Players start in the minor leagues, playing for a team run by one of the MLB clubs.