I think the issue might not be that he's not getting anything out of it - it's more likely that *you* aren't seeing the progress because Scratch is something he does on screen and it's hard to follow from the outside. A 9-year-old can genuinely get excited about this stuff, but if he feels like nobody cares about what he's made, he'll lose interest pretty fast.
Try this: after each class (or midweek), sit down with him and ask him to *explain* a block of code he created, even if it's something simple. It doesn't have to be about programming - he just tells you how he got the character to move or why he added a sound effect. You ask dumb questions on purpose ("but how does he know when to move?", "what if you did this instead of that?"). This keeps the conversation going, he feels like it matters, and he actually ends up understanding what he's doing better. It's like when someone explains something to you - that's when you really get it.
One thing other courses usually do: create a "personal project" for him separate from the classes. Something simple, a game or an animated drawing that he actually wants to make, not because someone told him to. It might take weeks, but he learns the blocks from the lessons and then applies them here. It completely changes the motivation when it's *his* thing.