"I took three classes this fall and I need two more to graduate," he said.
Castro, taken by the Astros in the first round of the 2008 First-Year Player Draft, re-enrolled at Stanford University in an attempt to finish his degree in sociology with an emphasis on business and the economy. As for the two classes he needs to graduate, he said he can take those anywhere.
"I'm real close now and will be excited to get that out of the way," he said.
Earning his degree would certainly be a proud achievement, but Castro hopes to earn his stripes this year as Houston's starting catcher.
Castro, 23, is coming to Spring Training as the starter, a year after he battled in camp with J.R. Towles for the Opening Day nod in 2010. He made his Major League debut on June 22 with a single off Giants ace Tim Lincecum and wound up hitting .205 in 195 at-bats for the Astros.
"All those experiences I had last year makes me a lot more prepared and ready for this season," Castro said.
Castro managed to get in his work in this winter despite his school commitments. He says he's ironed out his smooth left-handed swing and began an intense workout program with other professional athletes near his home in California's Bay Area.
All of it is done with the goal of establishing himself as the Astros' starting backstop and living up to the expectations the club had when they made him the 10th overall pick three years ago.
"I've put a lot of work in and ironed out some things mechanically," he said. "I'm in a place right now that I feel really comfortable. That's the best part is feeling comfortable up there, and that really puts you in the best place to have success."
The intense workout program Castro participated in this winter was at SPARTA Performance Science, a facility used by a handful of pro athletes in which workouts are geared to the individual athlete. Castro said it's designed for him to be in top shape entering Spring Training, instead of using the spring to get in shape.
"It's been a great program for me so far," he said. "There's a big group of baseball guys out there and workouts are tailored to the individual. It's really beneficial and it's going to help me this year."
Of course, nothing will help Castro more than his experiences from last year. He's learned from the struggles as much as the successes. He'll come to camp entrenched as the starter and not trying to win a job like he did last year, when he lost the Opening Day job to Towles.
Castro, a career .287 hitter in the Minor Leagues, admittedly struggled at the plate, but he hit .242 in his final 23 games of the season and wants to build on that when pitchers and catchers report in about two weeks.
"It was great getting to see what it's like up here and using everything I've learned and dealing with some of the struggles I had early on," he said. "That was good for me to move forward and see what it's like and build off of that. I'm feeling really comfortable and confident in my game, and I'm excited to get going."
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.