With high school football playoffs starting around the country, a leading medical body on Wednesday released a 306-page, NFL-funded report that found the sport not only has by far the highest rates of concussions at the interscholastic level, but also that the average high school player is nearly twice as likely to suffer a brain injury as a college player.

A panel of medical experts convened by the National Academy of Sciences analyzed a series of academic studies, with the most recent showing that college football players suffer concussions at a rate of 6.3 concussions per 10,000 "athletic exposures" -- each exposure representing a practice or game. For high school football players, the comparable figure is 11.2.

The report noted that most concussion symptoms disappear within two weeks as measured by current testing tools but that 10 to 20 percent of concussion sufferers "are still experiencing symptoms anywhere from weeks to months to years later." Across sports, 250,000 concussions were reported to emergency rooms in 2009 for people under age 19, up from 150,000 in 2001.

The findings are likely to heighten safety questions about football at the high school level, where athletes of varying levels of physical maturity -- some boys, some men -- collide with each other. High school athletes also lack the standard of care that is afforded to college and pro players, who have teams of neurologists and other medical experts managing their injuries. Many high schools cannot afford athletic trainers or proper equipment.

However, the report authors concluded that there's no evidence that even the latest helmet technology prevents brain injury -- challenging a notion held by many parents and coaches.

"The findings of our report justify the concerns about sports concussions in young people," said Robert Graham, chair of the committee and director of the national program office for Aligning Forces for Quality at George Washington University. "However, there are numerous areas in which we need more and better data. Until we have that information, we urge parents, schools, athletic departments and the public to examine carefully what we do know, as with any decision regarding risk, so they can make more informed decisions about young athletes playing sports."

Funding for the study was provided to the Centers for Disease Control Foundation by the NFL, which contributed $75,000 through the NFL Foundation.

In a statement, NFL senior vice president of health and safety policy Jeff Miller said: "We commend the IOM's recommendations and are proud to have supported the study through an NFL Foundation grant. We have been engaged on the key issues discussed in the report. It calls for more research into diagnosis and prognosis of concussion, longitudinal studies, and education programs to increase concussion awareness and understanding. We are investing in all of those areas and will continue to work in partnership with leading organizations on youth sports safety."

On Tuesday night, NFL commissioner Roger Goodell hosted a "Moms Clinic" at the Chicago Bears' training facility in Lake Forest, Ill. At the clinic, hundreds of mothers of players in local youth and high school programs learned tackling techniques as promoted by the NFL's youth football arm, USA Football, and heard from speakers who tried to comfort them in the decision to let their sons play football. On stage before a row of cameras, Goodell presented himself as an advocate and leader in youth sports safety.

"We want you to have the best information," Goodell told them, before presentations by Dr. Mehmet Oz and a female neurologist who discussed the recognizing of concussion symptoms. "We think our responsibility is to football but beyond that, too. It's about youth sports safety."

Goodell did not highlight specific rates of concussion in football as compared to other sports. Most speakers that followed him acknowledged the dangers of playing the game, while also encouraging parents to press local coaches and football boards to promote safer play, rather than pull their child out of the sport. Moderating a panel, Goodell's wife, former Fox News anchor Jane Skinner, said, "Kids are more likely to get injured riding their bike on the way to (football) practice than at practice."

Members of the National Academy of Sciences panel lamented the lack of data on concussion rates and vulnerabilities among children before high school age -- the Pop Warner level where considerable debate has arisen about whether flag football is the better alternative for kids engaged in football. Only in high school do most athletes begin to interact with trainers, who do much of the data collection.

At a news conference following the release of the report, panelists were at a loss to explain why the concussion rate for high school players was so much higher than for college players. One doctor speculated that high school athletes are more likely to report concussions because they are living at home with parents who are on alert, while another noted that developing brains are more vulnerable to harm and take longer to recover from a concussion.

While the findings in the report may make the NFL's goal of keeping kids in helmets more difficult, there were a couple of silver linings for the league.

Despite several high-profile suicides of former NFL players that drew considerable media attention, the panel concluded that there is no available evidence to document a link between concussions and suicidal thoughts and behavior. They also wrote that, "Whether repetitive head impacts and multiple concussions sustained in youth lead to long-term neurodegenerative disease, such as chronic traumatic encephalopathy, remains unclear."

In examining the effects of single and multiple concussions, the committee did find some observed impairments in memory and processing speed. A history of previous concussions was highlighted as a predictor of increased risk for future concussions, although the extent to which the risk is increased is unknown. Studies suggest the severity of concussion symptoms is greater in athletes with a history of two or more concussions.

To fill gaps in knowledge, the committee highlighted several areas for further research, including establishing a national surveillance system to accurately determine the number of sports-related concussions, identifying changes in the brain following concussions in youth, conducting studies to assess the consequences and effects of concussions over a life span and evaluating the effectiveness of sports rules and playing practices in reducing concussions.