HOUSTON, Texas (CNN) -- A 14-year-old high school football player collapsed here Saturday during practice and later died, school officials said.

The teen was the fifth football player to die during or after a summer practice or game this year in the United States, and the second this week.

On Wednesday, a 13-year-old middle school player in Georgia collapsed 10 minutes into a practice and died before he reached the hospital.

The deaths have focused attention on preparation and participation in strenuous activities, particularly during stifling hot summer weather.

Houston Independent School District spokeswoman Heather Browne said the Lamar High School player, whose name was not immediately released, had run six plays during a scrimmage when he collapsed inside the huddle at about 11:15 a.m.

RESOURCES

He was rushed to Texas Children's Hospital and pronounced dead nearly two hours later.

"The district, along with the principal and staff of Lamar High School express its deepest sympathy for the family," said Superintendent Dr. Kay Stripling. "Our thoughts and prayers are with the family as they deal with the tragic loss of their loved one."

Although the Houston area was under a hazardous weather warning for hot conditions, the cause of the boy's death is still unknown.

"He had a history of asthma, but he passed his pre-season physical," Browne said.

Georgia boy collapsed

A fellow player said the boy was breathing hard when he got back into the huddle after a play.

"You could tell he was trying very hard to breathe," the player said. "One of the coaches came over and he was laying on the ground face first. They asked him if he was having an asthma attack but he couldn't answer. They finally got his helmet off and turned him over, but by that time he was out."

Temperatures in Houston were in the low 90s at the time of the practice with a heat index of over 100 degrees.

An autopsy will be conducted either later Saturday or Sunday to determine an exact cause of death.

In the Georgia town of Monticello, about 53 miles southeast of Atlanta, 13-year-old Derez Bennett was participating in the third day of practice for his Jasper County (Georgia) Middle School team on Wednesday.

Bennett's father, Patrick Bennett, said doctors told him it appeared his son had a heart attack, and that heat was apparently not a factor. The boy's body has been sent to a Georgia Bureau of Investigation lab for an autopsy.

"They're really trying to rule out whether it was the heat or not," Jasper County coroner Billy Norris told the Macon (Georgia) Telegraph.

Bennett's mother, Lawanda Bennett, told the Macon newspaper that school officials told her "he wasn't feeling well so they told him to go to the sidelines and take his helmet off."

"They said his vision got blurry, and when the trainer went over to where he was, he collapsed. That's what I was told," she said.

String of deaths

The deaths of the two teens follow a series of others.

On August 6, Curtis Jones, a 35-year-old player with the Utah Lionzz of the United States Inside Football League, collapsed on his way to the locker room following a game in Las Vegas. Doctors reported that Jones died of a heart attack or an aneurysm.

On August 3, a Northwestern University football player, Rashidi Wheeler, 22, collapsed and died from bronchial asthma during a practice. Heat was apparently not a factor in Wheeler's death. Temperatures in Minneapolis were in the 80s at the time.

Just two days before, Minnesota Vikings player Korey Stringer, 27, died after a morning practice. Stringer's agent, James Gould, said an autopsy of the player showed he died of heatstroke.

Stringer had exhibited signs of heatstroke, including weakness and rapid breathing. Temperatures were in the 90s with stifling humidity in Mankato, Minnesota -- about 80 miles southwest of Minneapolis -- where the Vikings hold their training camp.

On July 19, University of Florida freshman Eraste Autin collapsed after a summer training session. He spent six days in a coma before dying of heatstroke. Temperatures in Gainesville that day were in the upper 80s, with high humidity.

Two players from Jackson High School in Stevenson, Alabama, died following workouts earlier this year in separate incidents a month apart.

The National Center for Catastrophic Sports Injury Research Annual Survey of Football Injury Research for the American Football Coaches Association, the NCAA and the National Federation of State High School Associations reports 17 heat-related football deaths between 1995 and 2000, all of them from mid-July to early September.