>>> I attended the TX H.S. Baseball Coaches Convention in January and found the simplest, most effective tool for teaching everything you are describing. Go to www.insiderbat.com and let me know what you think.
Albin Athletics <<<
Since your post was to promote a product rather than to discuss swing mechanics, my first inclination was to delete it. However, after reviewing the site's promotional video, I thought it might be beneficial to discuss one of the drills shown. In the "lead-arm" drill they demonstrated, the batter starts with a 'boxed' lead-arm (about a 90-degree bend) and then straightens the arm approaching contact.
Although many batting coaches teach this type of lead-arm drill, my study concludes this drill is counterproductive and not exhibited in the mechanics of the best hitters. As the video clips contained in the posts below shows, extending a boxed lead-elbow (like throwing a Frisbee) stalls the development of bat speed.
Role of the lead-arm