I remember hearing "back in the day" that boy's cursive was neater than print because they learned it later, and had developed better fine motor skills by that point (and it's easier to learn a new script than unlearn bad habits with an already known script). So maybe wait until he has better fine motor skills and teach him a different writing style?

If he doesn't want to learn the Palmer method (what you probably learned if you grew up in the US), then perhaps Getty-Dubay?