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]
(..) You trying to squeeze an inch in on me somewhere?. -Sir, no, sir. -Bullshit. It looks like the best part of you... ...ran down the crack of your mama's ass and ended up as a stain on the mattress. I think you've been cheated. Where the hell are you from, private?. -Sir, TeXas, sir. (..)1987 Full Metal Jacket