Slow and steady is perfectly fine :)

I've found it's sometimes easier to get them to write when they're working with something they're interested in. With my kids, when they were younger we did a lot of writing exercises in the form of roleplaying notes. We'd play our roleplaying game, and then I would get them to dictate to me a summary of the session as they remembered it, and then they would have to copy it out.

Eventually they got fast and familiar enough with the words and letters to write them out themselves.

Playful and less strict is a great way to approach things :D and yay for improvements :D