Coach's Eye is a great app for coaches. I used to help coach middle school throwers in the art of discus and shot putt... Most students have a difficult time controlling their bodies and being aware of what they are actually doing. You can use the Coach's Eye app to save videos and then play frame by frame back to the students or athletes. You have a lot of abilities to demonstrate good and bad form. 
Coach's Eye can also be used effectively in the classroom, specifically gym class. You can teach a new skill in a game and do quick videos of students demonstrating the skills. You can then go back and grade their skill or bring them over and show each student what they are doing and what they should be doing. Great for activities and perfect for weight lifting. This app will ensure good and safe lifting procedures by breaking it down and show students what they are doing versus what they should be doing.
This app is available on the Apple and Android market for a price of $4.99.
