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]
(..) Prue, don't give me grief when you get the phone bill. I was up all night on the Internet, and I didn't find anything. That poor girl. Oh, Piper, I'm sorry about the crack I made last night about your zit. That's okay. So you really can't see it? Like I said, it's huge. Something weird is going on. (..)1998 TvShow: Charmed Title: The Truth Is Out There... and It Hurts Season: 1 Episode 8