My experience with groups is that there is no discount/savings, and sometimes you even have to pay more than the advertised rate.
The deal is that they will guarantee your whole group will be on the same plane, and you can even book seats close to one another.
Some airlines will allow you to pay a deposit to hold the seats for the group, and then pay the balance about 30 days before the trip. That's another advantage over having everyone book online separately. When you do it as individuals, you have to pay in full when you book. And if there are 17 of you, you may not all end up getting the same fare. The lower priced seats are few in number, and once enough people have purchased them the price starts going up.
I have run 3 Boy Scout trips that required airfare. Our groups were between 25 and 45 people on the different trips. We never got a discount. I used US Air out of Phila this past summer and Spirit out of AC 2x before that. I spoke with SWA. but their fares come out too late for what we needed. We wanted to lock in prices more than 6 months out.
So, just be prepared. You will likely NOT get a lower price, just a guarantee that you will all be together.