HARTFORD, Conn. -- Southington High School football player Jon Kelleher collided hard with his opponent. After the game, he realized something was wrong.

Kelleher said, "When I went to do some schoolwork, I could tell it was bad. I couldn't do it, so I knew something wasn't right."

He had a concussion, which is the most common type of traumatic brain injury. It's when a blow to the head literally jolts and jostles the brain. Usually headaches, dizziness, memory loss and fatigue follow.

Kelleher said, "If I went to school and tried to read anything, I instantly got dizzy. I got a headache and couldn't focus at all."

Southington High School Athletic Director Eric Swallow won't let any athlete who gets a concussion back on the field until they pass the impact test.

The impact test is a computerized test that many high schools and colleges use to gauge if an athlete's brain function is back to normal.

In the beginning of the season, it's the baseline test which measures memory and reaction time. After a concussion, they take the test again to see how well the brain is healing and if it's back to its normal function.

At Conard High School in West Hartford, Megan Cummings was tested after her concussion on the soccer field.

Cummings said, "My head hurt looking at the computer screen taking it."

Her trainer Brian Elliot explained that an an athlete tries to remember as many words as possible from the test. There is also design memory which is remembering which direction the arrows and shapes were pointing on the screen.

Some athletes have to take the test multiple times before they are cleared to play.

Elliot said, "It's such an important tool because it can actually get us inside an athlete's head to see where they are in terms of their normal brain function."

Research shows that people who suffer from concussions are at a higher risk of getting another one and suffering a second blow to the head while recovering from the first can have catastrophic results.