The 6-foot-2, 200-pound Turner, who plays at Indianapolis Cathedral High, earned his Irish offer by running the 40-yard dash in 4.5 seconds last week, and he committed Sunday.
The question, though, is where he fits into the defense.
"He's going to be a big safety or a really fast linebacker, Indianapolis Cathedral coach Rick Streiff said. "It depends on how he fills out. He's 6-2, 200 pounds, and he's really long. He may wind up being a guy that is 235 pounds and play linebacker, and do it pretty well."
Turner ended his junior season weighing 185 pounds, but when college coaches visited during the spring evaluation period, he was up to 200 pounds.
If he continues to add weight, Streiff has no doubt about Turner's ability to play linebacker in Notre Dame's 3-4 alignment.
"He'd be a WILL (weakside) linebacker in that system," Streiff said. "He's not a kid that's going to line up and stuff a fullback, but he's a guy that will be a good flat defender, he'll range, he'll contain. I think he'll do those kinds of things. He's not a goal line-stuffer kind of guy, or not yet, anyway. He may work his way into that."
Several Big Ten schools recruited Turner to play weakside linebacker, but he could turn into a strong safety with the Irish.
However, he plays free safety for Indianapolis Cathedral, which allows him to showcase his athleticism.
"It's kind of unusual because it's not what he's going to be doing at the next level," Streiff said. "In our defense he is a cover-2 safety. He plays on the hash, he's a speed guy. We don't ask him to make a lot of tackles. He's mainly a pass defender for us."
Turner's speed was in question in his recruitment until he ran at Notre Dame's camp, but Streiff simply points to the final game of the 2010 season for anyone who questions it.
Stanford-bound class of 2011 four-star running back Remound Wright of Bishop Dwenger (Fort Wayne, Ind.) broke off a big run, but Turner tracked him down.
"John was able to run Remound Wright down on a long run to save a touchdown," Streiff said. "He's pretty fast. He's got good football speed, too. He's a good football player. He's rangy, he's long, he plays hard, he gets after it in the weight room. He's got all the intangibles."