The popular theory was that he was "too small" for the Big 12. If he had any shot at playing, he would have to get bigger and stronger and wait his turn behind the incumbents.
So when Garrett, 19, was thrust into a starting role when star shortstop Ian Kinsler injured his foot March 16, nobody expected the 5-foot-7, 135-pounder to produce like he did.
In the nine games that he was in the starting lineup, Garrett batted a team-leading .621 (18-for-29) with a double and nine RBIs. He also led the Tigers with a .714 on-base percentage. "It's always surprising when a freshman does that well," said Missouri head coach Tim Jamieson. "You don't expect that because the adjustment period that goes on. Particularly when you step into the heat of the season like he did. There was no lead up, he just kind of got thrown into it and he did very well."
He was a key component during the Tigers' 13-game winning streak, the school's longest since 1988, and their subsequent push to No. 20 in the national rankings.
Garrett was named Player of the Week for Week 8 of the season on an online poll. He was named the co-MVP for the month of March.
The switch-hitting Garrett currently leads the Big 12 conference with a .650 batting average against league opponents.
For the season he is hitting a team-best .476 (20-for-42) with 20 runs scored and 10 RBIs.
No other player on the team is hitting better than .400.
"He runs well and he puts the bat on the ball," said Jamieson. "He can bunt. He finds different ways to get on base. He's got a small strike zone which is a good thing. His role is to get on base, whether it be a walk, or get hit by a pitch or a base hit. It doesn't make any difference, we just want him to get on base."
He's certainly done that, as evidenced by his team-leading .586 on-base percentage.
"He's given us everything we thought he would, plus more," said Jamieson. "He exceeded our expectations offensively. He really had a lot of clutch hits during that streak. Adam was a big part of that because he hit over .500 during that streak and he played very well defensively."
A three-year starting shortstop at Sikeston High School, Garrett became known as a defensive whiz for the Bulldogs.
In his three years, Garrett and the Bulldogs compiled a record of 63-14, including two Class 3A Final Four appearances.
So Garrett is used to being in the spotlight and playing against the best competition.
"I was really happy about getting the opportunity to play and do my best," said Garrett. "My main mental approach was just to try to get over being nervous. Things just clicked and I saw the ball well and was doing really well."
Things are going so well for Garrett that even a 90-mile per hour fastball isn't anything special anymore.
"Last night a guy was throwing 92 and it just looked like a regular pitch," said Garrett. "In high school, when you're warming up to a pitcher, you're thinking, 'oh man, he's throwing hard.' Now, since we've been seeing pitchers that throw 90 all the time, you get used to it."
So hitting a 90-mile per hour fastball isn't so hard. Not so fast, says Garrett.
"It is a lot harder than high school because you're thinking what kind of changeup he has and what's his curve ball like, and not how fast he can throw," said Garrett. "You just have to be able to see the ball."
So what does the future hold for Garrett?
Currently the Tigers are 25-11 and 9-5 in the Big 12 Conference. Kinsler has returned to the lineup, forcing Garrett into his backup role.
But at least now, with his brief cameo for the Tigers, Garrett knows he can compete on the Division I level.
"We just want him ready to come off the bench if needed," said Jamieson. "But he's definitely shown that he can play at this level and that he's provided us with a lot more depth than we thought we had at the beginning of the season. I think he's going to be a real good second baseman for us when he has the opportunity to play consistently."