I thought for a minute, and then I remembered a conversation that I'd had with my father when I was about his age. He talked candidly with me about a money issue that I didn't fully understand at the time, but I felt really grown-up and special to be part of the conversation. So I invited him to pull up a chair and sit down. I explained to him briefly about the idea of a zero-sum budget, that every dollar should have a job. I explained the implication of taxes, that a salary of $48k a year doesn't mean you can spend $4k a month. I gave him some rules of thumb that I use - that for every $1 of take-home pay, $0.50 will be used for "needs," $0.30 for "wants," and $0.20 for "savings." I also showed him that sometimes those categories can overlap a little bit. I let him see some of the charts and graphs on YNAB and showed him how the budget helped keep us focused on our goals. The best part? He was totally engaged and interested.
(Of course, I prefaced this entire conversation with: "This is personal family financial information. You can talk about it with me or Dad, but you understand that you aren't to tell anyone else about what type of accounts we have, how much money is in them, or anything like that, understood?" He understood.)
He wants to keep learning about finance. And I really want to teach him. I'm just looking for any advice, pointers, or systems that others have used with their own kids (or that maybe your parents used with you) that helped you develop smart money habits and attitudes. He's an avid reader, so any books about money for teens would be great, too. Anything you can suggest, I'd be happy to hear it.

