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]
(..) whenever Johnny and i hang out the first item on our agenda is... whats going on with Lori? so you know its funny that didnt come up. it musta have slipped through the cracks we do, we talk about you all the time you remember the other day? i was saying how great Lori's hair always looks (..)2012 Ted