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]
(..) we barely scratched the surface. You cracked the code though, Sherlock. And maybe Dimmock can track down all of them now he knows it. No. No, I crack this code, all the smugglers have to do is pick up another book. SIREN BLARES Without you... without your assistance, (..)2010 TvShow: Sherlock Title: The Blind Banker Season: 1 Episode 2
(..) He's trying to communicate with his people in the underworld. Whatever was stolen, he wants it back. It's somewhere here, in a code. We can't crack this without Soo Lin Yao. Oh, good. Two men who travelled back from China were murdered. And their killer left them messages (..)2010 TvShow: Sherlock Title: The Blind Banker Season: 1 Episode 2