My son is 12 and throws pretty hard but he consistently releases high the harder he throws. I told him to bend his front knee more a la Tom Seaver. What do you think? What else can I look for?

It's not clear whether the knee bend mentioned is on launch or landing - sometimes the first challenge in helping someone with a question is to make sure you understand the terms of reference.

So rather than answer without enough knowledge, I will open this up for others to seek details.
I will say this - I'm not sure I would look at the knee lift as the root cause or solution to high or early release point - factors such as tightening the grip or over extending the stride length or rushing the body can all come into play when the mind decides to "throw harder".

Just be clear that many times a youngster's "mechanics" is not where we adult coaches would like it to be because there are "growth" issues, as well as lack of core strength. A short stride may cause him to throw high, but trying to get him to throw a-la-Tom-Seaver may be physically impossible due to individual anatomy and lack of core strength....this is quite common in 12 year olds. Why not focus on throwing slower with accuracy...then you begin the process of teaching him how to pitch instead of how to just throw hard. The craft of pitching takes many years...at 12 years of age he has plenty of time to develop and as he gets stronger (core) he will be able to maximize his stride and release the ball near or in front of his landing foot. But without video-taping and actually seeing what is taking place, it's hard to make a meaningful comment. Many times what you see is not what is taking place and what is really taking place you cannot see. As humans we only see 32 frames per second...in making accurate analysis in pitching, you need to see better than this...so video-tape and have someone that knows what they are looking at help you. But don't forget that what is applicable to an older teenager or adult does not always applly to a 12 year old, especially in pitching mechanics.

In the next Pitching Insider newsletter - coming in early Sept, I'm going to talk more about video taping - 32 fps is not fast enough. As for the age concern, Jose is absolutely correct - development rates and growth spurts affect young pitchers in ways not always obvious. Getting our players to mimmic pros is one of the greatest mistakes we can make as coach.