Re: formal "class" as a supplement to keiko?
Not aikido, but when I teach my judo class I talk them though the technique, then they practice with the drills I have laid out. I make sure to keep them working so hard they don't have time to chatter. If they have a question of course they can ask it and I will help that pair out with their question. Sometimes I will then stop the class to have them listen to the question and my response.
Talking is a vital skill required to teach. If you can't communicate with your students either criticism or praise they will never know if what they are doing is right, or just looks right.