Parents are concerned that children who have trouble in school will 'fall through the cracks' in the school system. [=will not be given the help they need; will graduate without anyone noticing that they are unable to do the work]
The program is meant to help workers who may have 'slipped through the cracks' [=who may have not been included in other programs] because of their age.
You ought to 'get cracking' [='get going; get moving'] on that assignment. [=you should start working on that assignment right away]
(..) Remember your ABCs-- "always be closing." ( gasps ) What the fuck is wrong with you, man? ( Cracks ) Hello! Will somebody please help me? Trent? Is that you? Come on. (..)2009 The Black Waters of Echo's Pond
(..) Man: These must be Pete's lobster traps. Woman: Sweet. Who's Pete? - ( Gunshot cracks ) - Woman: Oh, my God. Get off my island! Pete! What, are you nuts? It's me-- Anton. Oh. (..)2009 The Black Waters of Echo's Pond