Some suggestions that have worked for me:

Find a visual representation of articulations that you like. There are several floating around on the internet. There's a page in the Foundations book that has some ideas. I like to think of legato as a brick of sound, staccato a block with space in between, accent as a block with a triangular left side, marcato is a triangle pointing right. Think what the sound waves would look like.

Use Tonal Energy. Display it on a screen if you can. Have the band (or individuals) play their notes into the analyzer, compare the shape of their sound waves with your ideal.

You MUST hear individuals. Go down the row in class. It can be fast, just a measure or two. Develop the skill of giving short feedback to one student while you're listening to another play - so A plays, while B is playing you're giving A a quick adjustment, while C is playing you're giving B an adjustment, etc.