Here are three interesting videos about game design, they are not focused on instructional games but if you substitute “instructional game designer” every time they mention “game designer” you will learn a great deal about designing instructional games.
This presentation talks about the different genres of games.
This is a great top ten list that helps clarify what you should do before designing a game. (number , 9 and 8 are not very applicable but most of the others are…)
Here is an interesting take on “Game Mechanics”