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]
(..) and moved the camera around it. Bullet time was the technical hurdle. But the conceptual, you know ... ... nut to crack was the portrayal of the real world. Which was, oddly enough, the most bizarre part of the movie. Which was the place where ... ... horrendous biomechanical (..)2001 The Matrix Revisited