I'm traveling quite a bit this fall. Mrs. Swede is a severely math-challenged, so I'm still left helping Miss Swede do her (now 6th grade) math homework. Currently, Mrs. Swede takes pictures of Miss Swede's math homework and sends it to me via Facebook Messenger, and we chat via Skype.

That works, but I think I'd rather do whiteboard sessions with her to help explain the math better. I'm open to anything web-based, Windows-based, or Android app. Ideally, it would be free, but I guess I'd be willing to pay a small amount if it's a really good product.

IDroo looks like a very good candidate, but I'm asking this fantastic community for other suggestions. Thanks in advance.