There are many criteria to selecting the school that is worthy of the investment, and this is not an exhaustive list. However, consider these to get you focused on what is important to you.
Key #1) Golfing style
As with any topic or subject matter to learn, golf can be played in many styles. Most of them based on your personality and skill level. Some play aggressively, others, like me, more conservatively. But ultimately you have to choose a school or instructor that matches you.
Your skills, your personality, your style.
Key #2) Problem areas
I have trouble with slicing. Consistently I find that my shots slice to the right. You, to be sure, have at least one issue with your game or specific shots. You may want to find a school to address and help correct that shortcoming. If you come back from a long weekend and your slice has vanished, you would have had time (and money) well spent.
Key #3) Instructor to class-size ratio
This is a personal preference item. Some people learn in a group setting (even craze the interaction). Others of you need the attention that a one or two person class offers. It may also depend on what you are trying to gain from the school which one you actually choose.
Key #4) Price
For some this may not be an issue. Golf is your life and no amount of money is too much if you improve your game, and thus your enjoyment. For others, big obstacle. If you are considering a golf school then you know that most start above $1500. There are some “big name” instructors offering half day lessons for $10,000.
You know your budget. If you are price sensitive then, by all means, do not forget to add in travel, lodging, and food costs. Many times these “incidentals” can double the overall cost.
Key #5) Proximity
What is your traveling distance? Is your schedule tight so slipping off within 100 miles for a half day lesson is all you can squeeze. Or, are you planning your school around a vacation so distance is not really an issue. One plus of keeping tabs on those schools “in your own backyard” is when these offer last-minute specials you can jump on those quickly.
Key #6) Length of training
How long can you take off from your profession to pursue your passion? Like any good consultant would answer, it depends. It depends on whether you are looking for a long weekend, a one day seminar, or wrapping a vacation around your training. This is an important factor in choosing a school so compare wisely.