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What can Celtics expect from JaJuan Johnson?

If, like me, your first thought after the Celtics [1] drafted JaJuan Johnson [2] was, “Well, at least they got someone who could contribute right away,” then think again.

The C’s picked the 6-foot-10, 220-pound four-year collegiate power forward with the No. 25 pick in the first round of the 2011 NBA draft. In the five previous drafts, ever since the NBA banned high school players from joining the league until age 19 or one year after the graduation of their high school class, exactly 30 four-year college players have been drafted in the first round.

It could be better (Roy Hibbert [3]) or worse (DeMarre Carroll) than the 6-foot-7, 240-pound Booker, the No. 23 pick by the Wizards (via the Timberwolves [4]) in 2010. To get an idea of what the Celtics should expect from their first-round pick if and when the 2011-12 season [5] begins — and beyond — here’s how the seven other four-year collegiate big men have fared since 2006 …

2010 NBA DRAFT

No. 23: Wizards select Clemson’s 6-foot-7, 240-pound senior power forward  Trevor Booker

2009 NBA DRAFT

No. 13: Pacers select North Carolina’s 6-foot-9, 250-pound senior power forward Tyler Hansbrough [6]

No. 27: Grizzlies [7] select Missouri’s 6-foot-8, 212-pound senior power forward DeMarre Carroll

2008 NBA DRAFT

No. 12: Kings select Rider’s 6-foot-11, 250-pound senior power forward Jason Thompson

No. 17: Pacers select Georgetown’s 7-foot-2, 278-pound senior center Roy Hibbert

No. 29: Sonics select Indiana’s 6-foot-9, 251-pound senior power forward DJ White

2006 NBA DRAFT

No. 5: Hawks select Duke’s 6-foot-9, 250-pound senior power forward Shelden Williams [9]

No. 12: Hornets select Connecticut’s 6-foot-11, 235-pound senior center Hilton Armstrong

Not exactly a murderer’s row of NBA diamonds in the rough. Regardless of what kind of production the Celtics get out of Johnson, one thing is for sure: The Purdue product will be the only one of the seven four-year collegiate big men selected in the first round since 2006 to perform for a playoff team. How much he’ll contribute to that is highly suspect.