My son has that diagnosis- it doesn't mean a lot, I don't think, other than giving a label to explain that some things greatly disturb him and instead of it always coming out in the form of depression or anxiety, it can cause extreme moods of varyiing types and resulting disruptive behavior. Google adjustment disorder. The "mixed emotions and conduct disturbance" is kind of a sub-category, from what I found, because apparently there are other ways it can be exhibited. I found it useful in helping others to see that the behavior issues were a result of other issues, not the cause. If he's having behavior problems at school, this should help. Also, it would help a therapist in working with him.