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]
(..) Excuse me, baby. -Latrell, my man! What's going on, brother? -What's up, man? -Two apple martinis. -You hitting that, bro? -This is a tough one to crack. -Tiffany Wilson? The ex queen? Here. Drop a couple of these babies in her drink, man. Are you sure this will work? (..)2004 White Chicks