This is a nifty little video about the classical seat, some common problems, and exercises to help fix them. Very basic, but good for the beginning instructor, and the visual learner!
If that doesn’t work, use this URL: http://www.videojug.com/film/how-to-improve-your-classical-seat-in-horse-riding
Note: This is not professional advice, this is a blog. I am not liable for what you do with or how you use this information. The activities explained in this blog may not be fit for every rider, riding instructor, or riding center depending on their current condition and resources. Use your best personal judgement!