Originally Posted by SFrazeur
Ask for the school district's permission. They may not have posted rules against it, but there may be accepted rules or an understanding with them that this instructor is the only one allowed to teach for profit.
Are you willing to burn bridges with this instructor? If you are working with kids other than your own on a regular basis he/she might take umbrage to this.
Good point about liability and also above about the school district courts. Where I grew up, you could not use publicly paid for courts to make a profit, unless you were part of the town parks and rec programs. It wasn't physically posted on the courts however. I honestly don't know the rules where I live now, but my guess would be the rules are the same for the same reason; taxpayers are not building courts for individuals to profit from, regardless of how minimal the profit is.
That being said, if there are no rules against what you are doing, then continue to teach the kids! You are doing a good thing by spreading the game we love to the youth, and it is always good to have more future players. Plus, you are creating healthy habits which hopefully will continue for a lifetime. Regarding the other teacher and the time, if you are a better teacher, or cheaper, or more popular for whatever reason and more kids are going to you, well, hopefully that will force him to up his game and everyone will benefit by better teaching.