A useful tactic to get kids to think in the classroom is to do what I call going negative. I learned this way of thinking about a problem when I was a teenager, especially when trying to figure out faith. Going negative isn't new: Sherlock Holmes fans may remember how he took the same approach in asking why the dog didn't bark. So instead of asking why Jesus did x, or why the Church teaches y, I was constantly wondering, "why didn't Jesus do a" or "why doesn't the Church say b." Pondering (sometimes for years) the a,b & c that weren't said or done often shed light on the superiority (not just the option) of x, y & z.
I churned for decades over the fundamental problem of why God required the whole Jesus project instead of simply declaring us forgiven. God is omnipotent, after all. I suppose this is no problem for billions of Christians, but I had to grind through dozens of negative propositions to arrive at an understanding of Salvation History that meant something to me. I knew all my life that "Jesus had to die for our sins," but that was just a fact, like heliocentricity. I was in my late 20s before I finally understood Jesus' sacrifice in a way that mattered. Oddly enough, years of "but why not...but why not...but why not..." eventually illuminated a childhood experience with a broken window which was full of "but why nots." Once I sorted out the broken window, faith fell into place. I don't think I'd've ever acquired a motivating faith without having reflected on the "why nots."
In Catechism class the kids will sometimes make no real progress in answering a positive question, such as "why did Moses hit the rock with his staff?" They will readily say, "God told him to;" but reader, that ain't progress- that's parroting. If I say, "Yes, but why did God tell him to?" I typically get, "because the people were thirsty" which is just another bit of fluff. My temptation is to give them an answer, but they can often make progress through negative questions, such as:
Why wasn't it enough for Moses to just pray for water?
Why didn't God make water flow from the rock without the stick business?
Why didn't God just make the people's thirst go away?
Why didn't God put a lake ahead of them that they'd run into?
Why couldn't Moses go by himself to hit the rock?
Once a couple of kids give thoughtful answers to negative questions they never heard before, we can move forward again. Within the first month of class, the kids get used to going negative when their thinking stalls. They learn to perk up each time the negative questions start, and are stimulated by the oblique thinking that negative questions engender.
Typical negative questions I might ask:
Why didn't Jesus heal the paralyzed man as soon as he was plopped down in front of him?
Why didn't the paralyzed man's friends stay home and pray for his healing?
Why didn't the Prodigal Son's father interrupt his confession?
Why wouldn't the Pharisees accept that Jesus had healed the blind man?
Why didn't John the Baptist get married?
Why wouldn't Elisha come out and speak directly to Naaman?
Why didn't the little boy bring his bread and fish directly to Jesus?
Why didn't Jesus and the apostles eat any lamb at the Last Supper?
Why weren't Jesus' wounds healed up after his Resurrection?
Why didn't the stewards tell Jesus they had run out of wine?
Why didn't God take more than one rib from Adam?
Why didn't God take a toe instead of a rib?
At Mass why don't the people put the bread and wine on the altar?
I'd give you the answers- but you'll learn better if you work them out on your own.