The age restriction was the headline provision of a collective bargaining agreement the NBA and its players union reached in 2005, and it went into effect with the following year’s draft. Before then, prodigies like Kevin Garnett, Kobe Bryant, and LeBron James transitioned successfully from preps to pros and became superstars.

But some others quickly washed out of the league, costing the franchises that drafted them millions of wasted dollars.

When Representative Steve Cohen of Tennessee pressured the NBA to lift its age requirement in 2009, threatening to hold congressional hearings on the matter, league president Joel Litvin wrote in a letter to Cohen that the rule is a product of “business considerations.”

Mandating that draft entries be at least 19 years of age, Litvin said, is about “increasing the chances that incoming players will have the requisite ability, experience, maturity, and life skills.”

A Globe analysis of player statistics, draft positions, and scouting reports suggests that the rule has helped NBA franchises make smarter business decisions. The Globe compared the 51 college freshman who have been drafted in the seven years since the age restriction was implemented to the 29 high school seniors who were drafted in the seven years prior. The review showed that players have performed better as professionals after a year in college and that their draft positions have often differed significantly from their rankings in high school.

The players who spent one season in college have averaged more points, rebounds, and assists per game in the NBA than the players who were drafted out of high school did at the same stages of their careers. The college freshmen were drafted an average of 3.2 positions higher than the high school seniors.

Within each draft class of “one-and-done” college players, the Globe compared the players’ actual NBA draft order to their average ranking as high school seniors by four major scouting organizations — ESPN, Rivals.com, MaxPreps, and Scout.com. For example, the actual draft order of college freshmen in 2009 was Tyreke Evans, DeMar DeRozan, Jrue Holiday, Byron Mullens. When the same players were high school seniors, Mullens was rated first, Holiday second, Evans third, and DeRozan fourth.

In an average draft class with 7.3 college freshman, a typical player’s position changed by 1.8 spots after a year of college basketball.

The 25 percent shift in class rank suggests that despite advances, evaluating high school talent remains an inexact science. Andre Drummond, the fourth freshman taken in last year’s NBA draft and the ninth pick overall, was rated the number twoprospect in the country as a high school senior by ESPN and Scout.com but was not among MaxPrep’s top 100 or Rivals.com’s top 150.

Recognizing the value of additional scouting time, NBA Commissioner David Stern has said that he would like to raise the age minimum to 20, which would nudge the league closer to the waiting period it enforced in the 1960s: four years after high school.

When that rule was challenged in 1971 by Spencer Haywood, an American Basketball Association star who signed with the NBA’s Seattle SuperSonics only three years out of high school, the Supreme Court ruled, 7-2, that the league’s ban on young players constituted an illegal group boycott.

Affirming a lower court’s ruling, the Supreme Court held that “if Haywood is unable to continue to play professional basketball for Seattle, he will suffer irreparable injury in that a substantial part of his playing career will have been dissipated . . . and a great injustice will be perpetrated on him.”

The decision effectively ended the NBA’s practice of keeping players out of the league on the basis of age, until it applied the current restriction in 2006.

Pechman, the labor lawyer, said he would love to mount a legal battle similar to Haywood’s, though he would allege age discrimination, not a violation of antitrust law.

“Bring the case in New York,” where the NBA is headquartered, Pechman said. “I’ll file it tomorrow.”

But Noel appears unlikely to become the star plaintiff. He has given no indication that he would fight the league in court, and his focus now is on his recovery, according to Ken Hollingsworth, the Tilton School’s athletic director.