I don't think it's that important, to be honest. As long as his writing is tidy, accurate and legible, why does it have to be "joined up"? Nowadays, it's as important that they can type well and use programmes like Word.
One of the reasons I withdrew my DS from school is that he couldn't write. At almost 11 he had the assessed handwriting age of 4. He has suspected Mearles Irlen syndrom and his reading age at the time was only 6years. ALl day, everyday the school made a fuss about his handwriting. He kept getting work back to do again, had individual handwriting "lessons" every day while the other children were having story corner or free play time or less formal stuff of one kind or another. His teachers made a point of NEVER displaying his work in case it drew attention to his poor writing/drawing. It all conspired to leave DS3 a wreck. He will hardly put pencil to paper, nowadays, although his writing is gradually getting better. He has a writing age of about 6 now (he is 13.) I try not to make a big deal of it. We just plod on trying to find things that work.
DS4, who is 7, can't write at all and doesn't want to. I am just leaving it alone, really, for fear of putting him off by forcing the issue before he is ready. DD on the other hand, has lovely writing, rubbish spelling though, and loves trying cursive. We have a whole load of "copywork" stuff that goes along with the history projects and nature lapbooks that she loves. At the moment she is completing a page a day with little snippets about horses and ancient Egypt. The boys aren't interested in this at all.
If I were you, I would be quite happy that he can write nicely, without worrying about joining up. Lapbooks rule by the way, for a couple of years that was all we did, really, apart from sums. The younger two still do them, but DS3 thinks that he is too old for them now.