Since I have been in the third grade, I have had to reteach myself how to do subtraction without a traditional algorithm. The district I'm at initially adopted Investigations. Investigations for third grade uses number lines to subtract.
Each year, I go through a painful month of reteaching students how to subtract using a number line. This year, the incoming students I have are very use to the traditional algorithm. I have no problem using that strategy but when it comes to regrouping, most of the students honestly don't know what "borrowing" from the tens really means. I made a handout to give to parents to show another strategy for subtraction. It's basically the traditional algorithm but broken down more to show the process of how to borrow.
If you have other strategies for regrouping, I would love for you to share in the comments.