How about treating each child differently depending on what motivates the particular child? One size fits all strategies tend to fail most people.
I was highly motivated as a child by a small monetary reward, such as proposed in this thread. My parents paid me $1/day to attend an all-day learning program that I didn't like. But, that $1 made it worth it to me. Note: after inflation, that would be closer to $3 now. And certainly any monetary reward would have to be adjusted for the lifestyle the child is accustomed to. A poor child may love $3 while a wealthy child might scoff at it.
Other children are motivated by praise, or goals, or freedom, or the ability to make choices, or making learning fun, or encouragement, or challenges, or special time with friends/family, etc. Spend time with the child and learn what is the right motivation.
And at least for math, the key motivation may be just filling in a gap that is missing in their math education. One bad teacher can leave something important missing in their math skills. Then since everything in math builds, the child thinks that they are just bad at math and gives up. The motivation might just be a little help to fill that gap and show that they actually can do the math. For example, just look at the number of people that get PEMDAS wrong on social media posts. Anyone who messes up on such fundamental things like PEMDAS will find anything more advanced frustrating to impossible.
https://en.wikipedia.org/wiki/Order_of_operations#Mnemonics