I don't have studies but we found that "teach your monster to read" was great and enjoyed. It's UK focussed, about learning to read phonetics. It's essentially

I don't have studies but we found that "teach your monster to read" was great and enjoyed. It's UK focussed, about learning to read phonetics. It's essentially a series of mini-games tying a story together, and it was very engaging for my son at a similar age. Also it's a one off purchase. (Edit - on android, free online it seems) If that's not as relevant for you where you are, it might give some jumping off points for finding more like it https://www.teachyourmonster.org/teachyourmonstertoread https://www.teachyourmonster.org/teachyourmonstertoread