If you are going to cast to the school, I suggest you use your trolling motor to make your final approach. Don't run into the school Stay on the outside, about a cast's distance away. Cast all around the school with your spoon, jig, or plug. You're likely to take the larger fish from around the outside of the school. If you don't have a trolling motor on your boat position yourself upwind, and let the wind bring you in quietly.
Many fishermen use wire leader to keep from getting cut off.
I have never like wire, and personally think you'll get more strikes if you use a short piece of 40 to 50 pound monofilament. You may still get cut off once in a while, but you'll have a lot more fun. Also, try to avoid using shiny hardware in the line. You don't want mackerel biting you line in two. If you're trolling, don't run across or through the school.