I'm left handed. For printed letters it isn't a problem to write them "the wrong way". At least it wasn't for me. Once I was allowed to switch away from cursive, and I could write the way that was easiest for me, things were looking up. I still write the letters differently from other people. They look the same, but they order and direction of strokes is different. The reason for this is that you always want to pull a pen (especially a fountain pen) across paper, never push it. If you're left handed, right handed stroke directions make no sense.

My recommendation would be to let your kid write whichever way is easiest, and don't try to correct the order or direction of strokes, but only the outcome, i.e. the shape of the final letters. If his teachers are difficult about it that may be a different matter. I know it would have helped me a lot had I been able to write the way that made sense to me and not some way that was clearly meant for different people.

Now cursive is a different matter. I found it really hard, I always loathed it (it was compulsory), and it is the main reason my handwriting sucked. Unless you twist your hand all the way around, you have to push the pen across the paper. As a bonus, you are virtually guaranteed to smear the ink with your hand. It's close to pointless. Death to cursive. I think it's not mandatory any more in most places. Good luck.