What java design pattern to use to implement a school management system?

I have made a college level implementation of a school management system but it is not satisfactory according to me. I want to know the method in which commercial software are implemented. How they use design patterns and the layers of abstractions used in building a commercial software. If anyone can direct me to a place or tutorial which explains this, it will be greatly helpful. Please no JAVA web based systems. I all ready know PHP and am adept at it