"She gave me a speech and just told me that no man can tell me what I can or cannot do," Thompson said. "She told me that I could make something of myself and that football could be what helps me get to where I want to go."
The Albany (Ga.) Westover defensive tackle has done exactly that. He's the Rivals.com Junior of the Year, the nation's No. 1 overall prospect in the class of 2015, with offers from most of college football's power players. Among the early favorites for his services are Georgia, Auburn, Florida State, Alabama and Clemson.
And that size he used bemoan? Rivals.com National Recruiting Director Mike Farrell said its what helps make Thompson elite.
"Trenton Thompson is an absolute freak defensive tackle even though he's still raw," Farrell said. "Even without great technique, his quickness, size, strength and non-stop motor set him apart. He's that perfect 4-3 defensive tackle who can push the pocket, hold the line of scrimmage, shoot the gap and not get caught up in the wash working his way to outside pursuit."
As Farrell said, Thompson is just learning the game; he's been playing tackle football for only five years. And it's been about 18 months since started working closely with Westover School defensive line coach and former NFL defensive lineman Jeff Hunter.
"He's only scratching the surface, and I'm only scratching his surface and things he can learn," said Hunter, who played five seasons in the NFL from 1990-94. "He's got so far to go in terms of his potential. That's why I'm surprised he's become the No. 1 overall player, because he hasn't even started to reach what he's capable of doing."
As a junior, Thompson helped Westover make the third round of the Georgia State Playoffs while recording 83 tackles (38 for loss) and 12 sacks. Those numbers tell only part of the story of the impact Thompson can have on a game.
"For a big guy, he closes very well and changes direction quickly in pursuit," Farrell said. "I just love the fact that he makes so many plays now and still has so much to learn and such a high ceiling. He's a great combination of accomplishment and upside."
One question that always comes up regarding defensive tackles is just how long they can sustain maximum effort. With the pounding a lineman can take combined with their average size, it's not unusual to see them take a few plays off. Thompson said he prides himself in defying that stereotype.
"I can't take plays off because everybody is watching me," Thompson said. "My teammates look to me to set an example so I have to go 100 [percent] every game. If I get a little bit winded, I still try to do my best."
When asked whom he models his game after, Thompson points to former five-star defensive tackle Haloti Ngata, who won a championship last season with the Baltimore Ravens.
"He's the best defensive lineman in the game. I want to get to that level," Thompson said. "I watch his highlights before every game and just visualize myself making the same kind of plays. The way he gets off blocks and the technique he uses is something I try to copy."
As he continues to grow, the key for Thompson will be to stay hungry and eager to learn. Hunter said that won't be a problem for the player so dominant he's combined his name with the adjective treacherous for the nickname, "Trent-cherous."
"He's extremely humble and eager to learn," Hunter said. "That's why it's easy to work with him. He's just going to keep getting better the more work he puts in."
Thompson said the memory of his grandmother is one of the many motivating factors that keep him striving to be the best. This offseason he's planning on working so he can be even more dominant during his senior season.
"I'm working on my conditioning, eating better and making sure I have a healthy diet," he said. "If you put something in your head that you can do and work hard enough, you can do it. That's what I'm trying to do with my game, I want to be the best."
Thompson, who is set to take the SAT this weekend, maintains a 3.0 GPA and is hoping to major in physical education when he gets to college. The plan is to take football as far as it goes, and then give back and stay close to the game.
If all goes well, Thompson said he will make it to the NFL, but either way he hopes to keep the promise he made to his grandmother when he was younger.
"I never give up, not matter what the situation or what the score is, it's never too late to make an impact," Thompson said. "I've always tried to keep that fire going and to make my family and my city proud."