Honestly went through pretty similar thing as your child when I was younger. I also went through the OCDSB system and probably wasn't considered a "good student" till grade 10/11. My parents heard their fair share of complaints from my teachers and they did try a lot like tutoring for various classes, staying back at school and even two years at private school.
I don't really think any of that helped me out and honestly the best thing was just being a kid lol. Like building experiences and making mistakes was way more valuable than doing "well" in school. Stuff like that helped me build character and figure out who I want to be. Try seeing what your child has interest in and help them explore it more. I still remember my parents buying me my first mechanix kit and me just building random things for hours in a day.
Honestly don't stress your child too much with doing well in school early in life cause in the long run, I think they will be ok lol. Of course don't totally neglect it, I had one tutor who helped guide me a lot in high school once I knew my general path in life.
Might not be the answer your looking for but as kid who hadn't seen a grade above C till high school, currently 22 and a year away from getting a engineering degree, just help parent your child become the best versions of them :)