Before his Thursday-night gig at Regattabar, pianist-composer Steven Feifke made a Wednesday visit to his alma mater, Lexington High School. The 2009 grad, who’s now playing in New York City, gave a master class to young musicians and listened to the school’s honors jazz combo. He said the kids were playing at a “remarkable level.’’ Lexington is known for producing creative superstars. Other grads of the high school include comedian-actress Rachel Dratch, singer-songwriter Matt Nathanson, musician Amanda Palmer, and comedian Eugene Mirman. Feifke had plans to stick around Boston on Friday to record an album.