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I spoke to several teachers for 1st and 2nd grade and they all shuddered and said, "It's really hard!" I used the tips they gave me to no avail. I've tried manipulative, diagrams, and legos. My son wants to know why he can't just count backwards.
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Amy
Mom to three very active girls Anna (15), Kayla (12), Maya (9).
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Also, I don't see a really good reason not to let him count backwards for now, if he can do it accurately. If he makes a lot of mistakes, it might show him that counting backward isn't really efficient, and that he might need to revisit borrowing/regrouping.
Are you using an actual curriculum, or are you making up your own? how have you used manipulatives to show him? Maybe we can suggest new ways to use them?
ETA: cross posted with annette marie  dd used 10s rods and cenitmeter cubes to learn regrouping, too.
This is what helped my son grasp it. 218, for instance. "So, can you take 8 away from one? No? That's right, because 1 is smaller than 8. So what do we do? We borrow from neighbor 2 over there, just borrow one. That goes right in front of your first 1, and 1 next to 1 is 11. And can you take 8 from 11? Yes!"
It's probably the "wrong" way to teach, but that's how he first learned to understand it, and then as he learned about regrouping things, the two ways connected.
Personally, I don't really see a difference between borrowing and regrouping other than the terminology. You don't actually do it a different way, right?

I spoke to several teachers for 1st and 2nd grade and they all shuddered and said, "It's really hard!" I used the tips they gave me to no avail. I've tried manipulative, diagrams, and legos. My son wants to know why he can't just count backwards.

This is what helped my son grasp it. 218, for instance. "So, can you take 8 away from one? No? That's right, because 1 is smaller than 8. So what do we do? We borrow from neighbor 2 over there, just borrow one. That goes right in front of your first 1, and 1 next to 1 is 11. And can you take 8 from 11? Yes!"
It's probably the "wrong" way to teach, but that's how he first learned to understand it, and then as he learned about regrouping things, the two ways connected. 
My big issue is getting my 8yo to IMMEDIATELY mark out the number in the 10's column and put one less.
DS2 has always struggled. We tried MUS when he was younger, and regrouping confused him for both adding and subtracting. I finally just backed off and approached it again every few months until it looked like he was understanding. I don't think he really "got it" until he was about 10yo, and that was fine. What's the hurry, ya know? He's a smart kid; his strengths just lie elsewhere.
The term "borrowing" is being phased out because it implies that something will be 'given back' or 'replaced' and that is inaccurate. Borrowing and regrouping are the same though and the terms are still used interchangeably. There are different ways to regroup and it may just be that you have to find the way that makes most sense to him.
What types of things have you tried? Unifex cubes can be really helpful but if he has a firm understanding of coin value using dimes and pennies are really great. It can offer a great representation of place value as well as the need to regroup.
Left to Right Subtraction
The second standard method of EM is left to right subtraction, the way one might well do the problem mentally, but carried out with paper and pencil. Here "left to right" refers to the decomposition of the second number. In the example at right, 32558, the 58 is decomposed as 50+8. The individual subtractions are done mentally.
325
 50

275
 8

267
3 2 5
 5 8

58= 3
25= 3
30=3
30030 =270
2703= 267
He's very fast doing it this way. He "got" negative numbers from a very young age, though. It's just another way of showing that you don't have to stick with the "official math teacher" methods. If you think he might be interested in learning about negative numbers, you might whip out a /+ number line and show him how this works.
It may help to use numbers that are too high to use fingers for and to have a paper with a tens and ones column. When dd learned subtraction I used legos linked as ten sticks and I had her keep the ten sticks in the tens column and the ones in the ones column. When she regrouped I had her physically break the ten stick into ones and put them in the ones column then I modeled for her what that looked like with the algorithm. We only did two or three problems a day because they were time consuming. After a few days of practice with hands on problems only I had her do both the hands on and the algorithm together. I found that she needed to have the numbers in each column separated and labeled until several days after she started doing the work on paper only. It took about ten days for her to move to paper only, but once she did she really had it down and does the work quickly and easily.
My big issue is getting my 8yo to IMMEDIATELY mark out the number in the 10's column and put one less.

My 8yo doesn't seem to understand what she's doing when she regroups. I made up a flow chart for subtracting doubledigit numbers and that resulted in a huge change from 'I can't do this' to 'I can follow a chart.' But I think there's an aha moment coming any day now...
I think math teachers changed it to "regrouping" in order to make it more clear to the student exactly what is happening and why  that you aren't crossing out numbers and adding ones and all that just because it works, but to teach them how it works. But if it's easier for the teacher (in the case of homeschooling, the parent) to explain it as "borrowing," I don't think it makes a bit of difference. I understood what was happening when I learned how to do it, even though it was called borrowing and not regrouping . When I taught my kids, I used the two terms interchangably, because I figured that if I only taught them one, they might be confused if they ever encountered it called the other.

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Amy
Mom to three very active girls Anna (15), Kayla (12), Maya (9).
In other words, regrouping refers to either constructing or deconstructing a unit of greater value (eg. making a ten from ten ones, or making ten ones from a ten). So it's a more useful word, and demonstrates the common concept of constructing or deconstructing units of place value.
My favourite way to teach regrouping in subtraction is to use money. Take a sheet of paper turned sideways and divide it into columns for dollars, dimes and pennies. Ask your child to place $4.35 in dollars dimes and pennies in the corresponding columns. Then ask her to take away 8 cents. She'll look at the 5 pennies and hopefully she'll see that there aren't enough pennies, and that one of the dimes needs to be traded in for ten pennies, allowing that value to be "regrouped" into the pennies column. Show her how you would write that process if you were doing the problem on paper. You've made $4.35 into "four dollars and twentyfifteen cents." Now there are enough pennies that you can remove 8.
HTH.
Miranda
Mountain mama to two great kids and two great grownups
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