I think this is a great way to get your kids to have a habit of self-learning. In my opinions, this is the single most important skill a kid can learn.
Every time my little cousins ask me something they want to learn, I go with "Let's search for the answer together" and guide them on how to do basic research. Sometimes I ask them follow-up questions if they find the topic interesting so it gives them a sense of accomplishment. Takes little time and effort but teaches the most valuable skill.
I think it's a great way to ensure that the only motivation your kids have is external. "What's the point of doing X is no one offered me a phone for it"
When I was a kid, I heard that some friends were getting money from parents as a reward for good grades. I always had good grades so I suggested to my mom that I should get money for good grades. She said "No, because then you'll get used to only work hard when I'm offering you money". At the time my take away was just "no money, got it." But now I think it was actually an insightful observation.
Good luck teaching a small kid the concept of self-improvement as an investment into the future. You have to reward kids to create habits. They don't have the experience or the knowledge to think far ahead. The best way to reinforce a behavior is immediate reward, not a promise of "better future". The reward can be something as simple as "a sense of accomplishment" or as big as a phone as long as the perceived value of the reward is proportional to the achievement and effort.
Now re-contextualize that as if it were an employer/employee relationship. That's actually a pretty messed up lesson to teach a kid about negotiation and self worth.
It teaches you that you should _also_ consider your own long term goals, as opposed to only chasing the someone else's short term goals. I think it's a great lesson to teach a kid about self-worth.
This seems like someone else imposing their own long term goals onto you because they allegedly know better.
You didn't describe any explanation of why good grades are an important step towards your own long term goals.
I'm not saying that paying for grades is a good way to motivate kids. I'm saying that framing it as "I won't pay you because it'll make you lazy" is a very weird way to teach a kid about long term payoffs.
I think this is a great way to get your kids to have a habit of self-learning. In my opinions, this is the single most important skill a kid can learn.
Every time my little cousins ask me something they want to learn, I go with "Let's search for the answer together" and guide them on how to do basic research. Sometimes I ask them follow-up questions if they find the topic interesting so it gives them a sense of accomplishment. Takes little time and effort but teaches the most valuable skill.