Castillo, who turned 18 in February, appears to be the clear-cut favorite on this list. The Dominican right-hander was signed by the Rangers in 2005 for an estimated bonus of $250,000. After making just one start in the states in 2006, Castillo appears ready to make his full-time U.S. debut this season.
The hard-throwing youngster possesses a mid-90's fastball to go along with an advanced slider. Castillo is currently working on his changeup in hopes that it will become his third above-average offering.
Though Castillo will begin the season at extended spring training in Surprise, he will join a club – whether it be Rookie League, Short-Season, or Single-A – at some point in the season. Being Castillo's first year in the states, he may go through a slight adjustment period both on and off the field. However, it appears likely that Castillo will be considered one of the top prospects in the Rangers' organization by this time next season.
2. Doug Mathis, RHP
The Rangers have already displayed their confidence in the right-hander's abilities by sending him to Triple-A Oklahoma to begin the 2007 campaign.
Mathis, the Rangers' 13th round pick in the 2005 draft, has rapidly improved in every facet of his game since his debut with Short-Season Spokane in the summer of 2005. The Mizzou product struggled at the outset with High-A Bakersfield last season, but finished strong and earned a late-season promotion to Double-A Frisco. Mathis was recently assigned to Triple-A Oklahoma on the heels of a phenomenal performance in spring training.
The 23-year-old native of Arizona works with a four-pitch repertoire. Mathis' fastball, which has good sink, has seen an increase in velocity over the past year, as it now tops out in the 92-94 MPH range. The spike in velocity allows Mathis to climb the ladder on a hitter to get strikeouts. Along with his heater, he also uses a rapidly improving curveball, an above-average slider, and a change of pace.
3. Zach Phillips, LHP
Phillips became well known to many Rangers fans after his outstanding debut with the Rookie Arizona Rangers in 2005. In 50.1 frames with the AZ Rangers, the southpaw struck out 73 hitters while walking just 13.
The former draft-and-follow signee bookended a rough 2006 season with a strong start and a strong finish at Single-A Clinton. Phillips held opposing hitters to a .222 average while fanning 38 in 28 innings in the final month of the '06 campaign.
With an upper-80's fastball, a very good curveball, and a solid changeup, Phillips has the pitches to succeed in the minor leagues. Because the 20-year-old has shown the ability to regularly miss bats and – as shown while allowing just five home runs last season – keep the ball in the park, Phillips is an excellent choice to enjoy a breakout season in 2007.
Zach Phillips checks in at number three on the list
4. Brandon Boggs, OF
Some players just look like big-time prospects. Brandon Boggs would qualify as one of those guys. The 6-foot-0, 190-pound outfielder has what scouts would describe as a "big league body".
An exceptional athlete, the 24-year-old Boggs has always had the tools to succeed in professional baseball, but he has yet to consistently produce. In parts of three seasons in the Rangers' organization, the Georgia Tech product has never hit above .261. Boggs has also been bothered by various ailments, as he has not played in more than 85 games in any of his three professional seasons.
Boggs appears to be fully healthy entering the 2007 campaign, where he will start at High-A Bakersfield. The former Yellow Jacket showed signs of breaking out late last season, as he hit .280 with five doubles, three home runs, and three more walks than strikeouts in the season's final month.
5. John Whittleman, 3B
Coming out of Kingwood High School in 2005, John Whittleman was widely regarded as the top high school hitter in the state of Texas. The infielder was said to possess a great deal of raw power, the ability to spray the ball to all fields, and excellent plate discipline. As premature as they may have been, these accolades prompted comparisons to current Rangers third baseman Hank Blalock.
A solid debut with the Rookie League Arizona Rangers earned Whittleman an opening day spot on the Single-A Clinton LumberKings' 2006 roster. Though Whittleman struggled for most of the season – outside of July, in which he hit seven home runs – the third baseman was praised for his ability to stay patient despite struggling at the plate.
Making his second tour through the Midwest League in 2007, the 20-year-old stands a solid chance to bring his performance up to par with his outstanding tools with the bat. A productive 2007 season could make Whittleman one of the top position prospects in the Rangers' organization.
6. Freddie Thon, 1B
Many avid followers of the Rangers' minor league system would be surprised to know that Freddie Thon hit .321 in 53 games with High-A Bakersfield last season. Thon did so, but he hit just two home runs while taking only five free passes in 218 at-bats with the Blaze.
But the first baseman isn't totally devoid of power. The native of Puerto Rico hit 12 home runs while slugging at an impressive .519 clip in 54 games with Short-Season Spokane in 2005. Despite his low home run totals with Bakersfield in 2006, Thon did show gap power, smacking 16 doubles.
The 6-foot-2 first baseman showed solid power at times during spring training and could be regaining his power stroke from 2005. But Thon, who walked just 15 times in 479 at-bats between Single-A Clinton and High-A Bakersfield last season, will have to become more patient for him to move up on the prospect list.
7. German Duran, 2B/SS
Playing with Double-A Frisco this season, middle infielder German Duran returns home to the Metroplex, where he starred at Forth Worth's Paschal High School, TCU, and Weatherford Junior College. The 2005 sixth round pick flew under the radar with High-A Bakersfield in 2006, as he proved to be solid in every facet of the game. Duran hit .284 with 31 doubles, 13 home runs, and 15 stolen bases.
Duran has a surprising amount of power for a 5-foot-10 middle infielder. He finished with a flourish in 2006, hitting seven home runs over the final month of the season. Aside from his above-average power, Duran has good speed and the potential to become very good in the field.
Duran's wide range of skills allows him to be inserted into a number of spots in the lineup, making him a more valuable offensive player. The Rangers believe that Duran is worth keeping an eye on as he returns home for the 2007 season.