How do you turn 200,000 + 40,000 + 6,000 + 500 into 246,500 instead of 2,465?
Most  of my children have had difficulty learning to order these big  numbers.  Personally, I wonder if this lesson group should be in a later  book, but it's in Beta, so we deal with it.  Here's what I do. 
I have them turn lined paper to the side, so  they can write one number in each lined column. I have them write the biggest number first, ie. 200,000. It takes SIX  columns to write it out.  I mention that you have to think about these big  numbers right to left, which is backward from reading, so it makes it  hard.  I use my fingertip to block out most of the number and say "units", move it to the left slightly, "tens", repeat movement, "hundreds" etc.   to teach the names of the places.  I tell them that they can count the number of digits to make sure it is the same as the one printed on the page. 
Then I have them write the next  number (40,000) underneath the first, UNITS FIRST!  I know it's  backwards from the usual way, but it's what worked for me. That way  units end up under units, tens, under tens, etc. I cover the number  again, and verbally point out that the units are lined up, then the  tens, then the hundreds, etc.  Then they write the next number, units  first, (6,000), then the next, units first,  (500).  Then we add the  units, the tens, the hundreds, etc, to get the right number.  I emphasis  that in this kind of problem, the answer must have the same number of digits as the largest (and usually it's the first written) number in the series they are to add.
  Some  of my older students overheard me teaching this and came to say that it  was the hardest part of the book.  They also said that when these  problems come up (very infrequently) later on, it seems much easier than it does when you are first learning it.  I love spontaneous encouragement!
  Also,  I do not make my students *master* this skill like I do math facts.  It is not really used much after these lessons and, like I said at the beginning, it is a higher  skill, in my opinion, than is needed at this level.  It comes much more naturally  later on.