Thank you so much for your responses. They are super helpful and give me some very important points to consider. However, when I started this thread late last night, I left out some important details about the business model. Here are a few points of clarification:
1. This business would be more or less "under the table", just as a kid mowing his or her neighbor's lawn would not pay taxes. I know that "legal stuff" will become a concern as the business grows, but much of it would surely be helped by the fact that this is not a direct boss-employee relationship. I don't know the specific legal details of this, but I could essentially sign a contract with the parents, stating that they are ultimately responsible for the worker in terms of legal stuff (many parents in this community are very hands-on, and would be thrilled to contribute in this way).
2. Each worker provides his or her own equipment, and is responsible for its transport and upkeep. Each worker will either have their own means of travelling between jobs (such as loading their mower into a van) or will only work within walking distance of their home. This policy seems harsh, but I do not think that it's unreasonable; they are making around $20 an hour, more money than the average teenager could dream of making at another job.
3. Employee retention is quite possible. I just graduated high school, and I know MANY people that would work for the business. Of course, upon realizing how tough the work is, many of them will decide not to do it. This job is not one that everyone could do. But I am confident that I will find a team of workers who is comfortable with more demanding work for better pay. For example, my little sister (who is a freshman in high school) just learned how to mow yesterday, and she mowed 5 lawns on that day!
4. If I, the leader of the business, do my job effectively, quality control should not be a huge issue. There are three reasons for this:
A. First of all, clients are quite forgiving, as long as I communicate well with them. For example, one time I simply forgot to mow a lawn (embarrassing), and I called the client as soon as I realized it, which was 5 days after I was supposed to mow it. I apologized profusely, took full responsibility, and offered to mow that day for half price. He was completely forgiving and even still paid full price.
B. I am in the process of writing a lawn care manual for my workers. It will tell them exactly what to do in great detail, and they will be expected to follow it exactly. Again, not just any teenager will be able to do this, but I am confident that a select few reliable workers will accept the greater demands for greater pay.
C. I have my family as a support cushion. My mom helps me manage the business and helps me pick up slack when I need to. She is even taking over the business for the autumn when I go off to college! Her, my brother, and my sister all love to mow.
4. This business will be rooted in the friendly relationship I have with each client. Some of my clients come outside to talk to me each time I'm there. They just love the idea of a young entrepreneur. One time when my mom was mowing a lawn (she mows when I need someone to, and she does it for charity), she started talking to a neighbor, and then another neighbor, and then another one. It was an odd social gathering. I believe that clients eat this social stuff up.