With a month of the season in the books, rookies are making impacts on their teams across the majors. For some, their arrivals and performances were expected; others have been pleasant surprises.

I’ll be keeping track of this season’s rookie class in this regular rookie report, monitoring their performances and possible trade stock for when the July 31 trade deadline approaches. So here are the top 15 rookies in the major leagues right now based on how they are performing this year, as well as the next 15 ranked in chart form below.

For the first installment of the rookie report, click here.

1. Shelby Miller | RHP | Stock: Up

Miller is pitching up to the expectations of a first-round pick (picked 19th in 2009). After earning a spot in the rotation out of spring training, he has posted a 3-1 record with an ERA of 1.44 and a WHIP of 0.84. Miller is a strikeout/ground ball machine. He pounds the strike zone with a 91-95 mph fastball with nasty sink and provides plenty of ground ball outs. He consistently gets ahead of batters, which sets up a devastating 12-6 curveball. He’s the early front-runner for NL Rookie of the Year.