In the interest of trying to write more, here's a thought I had. I'm not sure how far into it I can explore, because it seems like just a small thought, but I'll try to go as deep as I can.
While I worked at the day care, I was constantly tying shoes. Why do parents keep buying shoes that tie for children that don't know how to tie them? Is it because they want to retie them multiple times a day themselves?
It's so that the kids can learn to tie, one might reply.
Yeah, that's not practical. In today's world, there's no time for that. When the shoes go on the feet, that means it's time to go. Ideally in that situation, a parent could announce that it was time to leave, tell a child to go put on his shoes, and then wait patiently until the child has his shoes tied. In reality, a parent doesn't have the time or patience to wait and inevitably winds up tying the shoes herself.
The Montessori way would be to never buy clothes or shoes that a child can't put on my himself (okay, past infancy). To teach shoe tying, a parent could provide, during down times only, one of their own shoes or a tying frame and slowly model. Shoes for a child that tie would only come after tying is mastered. It might even be considered an incentive for learning. Child asks for shoes that tie? They must first demonstrate that they can tie the shoes.
Montessori curriculum uses dressing frames to assist children in learning these practical life lessons. Again, they're used during down times, not at the time a child is expected to dress herself. As far as shoe lace learning is concerned, here is both a lacing frame and a tying frame. Here's a video of the actual lesson a Montessori teacher would give using the tying frame. I love how everything is done multiple times to reinforce each action. (I've linked to Nienhuis because their pictures are nice, but you could definitely make them yourself using fabric, ribbon, and an old picture frame from the thrift store. Michael Olaf made a gorgeous one while teaching in Bhutan. Or, you know, whatever. Cardboard and cardboard boxes work just fine.)
Or if your child is struggling with his fine motor skills and just needs to get the right movements down first, you can always turn tying into a gross motor activity by using a giant shoe or giving him a jump rope.
And if the method is difficult, there are a myriad of alternative ways to tie shoes. One of them will surely be easier for your child than the traditional method! There are a lot of videos on the Ian Knot, and it sure does look promising!