Can you describe prescriptive and descriptive analyses?

I train graduate students to be teaching assistants. One of my graduate students is studying Public Policy Administration. He lectured on the difference between prescriptive analysis and descriptive analysis. Today he had to review these words from last week by asking questions, eliciting information, thus getting the students to interact. This style of teaching is quite different than in other cultures.
It took like 20 minutes for us to understand the differences again. His English is good, very good, but explaining concepts in simple, every day English, is a challenge. He's from Brazil, so he tends to use formal language.
In case you were dying to know, prescriptive analysis is the plan before you create a policy. Descriptive comes afterwards, the evaluation. However, it's tricky because they constantly overlap. (Kids are dropping out of school. Let's provide milk. This helps but they're still dropping out. Let's provide food.)
I've had this class play Catch Phrase, my daughter's favorite game. You have a word and you have to get your partner to guess the word just by giving hints, synonyms, examples, etc. It's quite fun and challenging. If any ESL teachers out there have other techniques to improve fluency, not just vocabulary but the ability to rephrase ideas in simple language, please share them!