I pulled an interesting observation and technique from Sol Stein's book Stein on Writing. Simply put, Stein suggests using The Actor's Studio Method to create conflict in the scenes you write: give your characters different scripts.
Here is an example to use in your classroom:
Select two students willing to improvise a scene. The script which you will give each is not a sheet of paper with lines pre-written. They'll make up what they actually say. What you will give them is the intent of the character in that scene. Don't let them know each others intent (script).
For our purposes here assume that Character A will be play the teacher and Character B will play the student.
You tell Character A no matter what do not agree to anything the student asks. You will not agree because this student's parent has phoned you and told you the exact opposite of what he/she says...but they asked that you not tell their child that they called.
You tell Character B that they truly left their assignment at home and they need to call their parents to drop it off. If it isn't submitted today you will fail for the year--this particular teacher has allowed his/her favorites to do this in the past and you have never asked for anything in the past from him/her.
And then allow them to improv and play it out. You don't know what will be said specifically, but it will demonstrate to your class how conflict can be thought about and written--give your characters different scripts.
Many writers do this intuitively, even the writers in our middle school or secondary classes. What is especially interesting about this technique is that if you chose two different students to play the teacher and the student then the story would play out a little differently.
You can create these situations out of anything--it is also rewarding to ask your students to create two opposing intents and then have two other students from class play it out in front of the class.