We hear the term "sophomore slump" often and I wondered if this idea had substance, so I compared some first and second year stats of the All-Rookie team of Channing Frye's class. (As an aside, the only player drafted ahead of Frye who wasn't on the All-Rookie team was Martell Webster.) These ten players are Bogut, Frye, Paul, Villanueva, D. Williams, Felton, Gomes, Granger, Head, and M. Williams.
One of the most interesting stats was in games played. Half of the players logged fewer minutes their second year than they did as rookies. Some were substantial drops: appearing in at least ten fewer games were Bogut, Paul, Villanueva (dropped from 81 games to 39), and M. Williams. I assume these were all injuries rather than coach's decision. Frye appeared in only 65 games as a rookie, second low to Gomes. The next year Frye was in 72, Gomes in 73. D. Williams and Head were in 80 games both years. The first year average was 76.4 games, second year 69.8 (and throwing out Villanueva's second year it's still fewer at 73.2.)
Minutes per game increased for everyone except Villanueva and Head. In his second year Frye averaged fewer minutes than everyone except Villanueva.
Total points per game went up for everyone except Frye & Villanueva, but the average increase was less than 3 points per game. The biggest jumps were by D. Williams and Granger with over 4 points each, but both had big increases in average minutes played, Williams up 8 and Granger almost 12.
Only six players increased their field goal percent and some of those were minimal increases such as Head's .004 rise. In fact the average fgp decreased from .451 their rookie year (Frye's was .477) to .450 the next year (Frye = .433). D. Williams had the largest increase, but his rookie year he had the second lowest fga of the ten. (Frye went from third to tied for 8th - his drop was the largest.)
Free throw percentage increased for all but three players. Two were under 70% as rookies (Bogut, Head) and two were over 80% (Frye & Paul). Five were over 80% their second year, only one under 70% (Bogut).
I pulled all my stats from basketball-reference.com and there are lots more that I could have used, but I thought these were adequate for a brief look. I won't say that "sophomore slump" doesn't exist, but I will say that it doesn't seem to affect most of the top rookies - except perhaps in a tendency to be more injury prone.