To be clear: I believe that it is the joyful privilege of Christians to pray for "the sick, the friendless, and the needy" and for "those in any kind of trouble" (both quotes are from the Book of Common Prayer, 1979). I believe such prayer may and ought to include specific petitions for specific outcomes. I also believe that God can and does act in the lives of those who pray and those who are prayed for in such ways as effect their healing, and that such healings often cannot be readily explained by medical science and may indeed, from a perspective of faith, be classified as miracles.
That said, I must confess that I get a little queasy when I hear language along the lines of "prayer works."
A screwdriver certainly works to drive a screw. A hammer works to drive a nail. A lawn mower works to cut the grass. There is an evident and expected outcome to the use of each of these tools, provided that they are in good condition and employed under appropriate circumstances by a knowledgeable user.
Last winter I fell and hurt my knee. A friend recommended an ointment called Blue Emu. I got some and used it and experienced temporary relief from the mild pain in my knee. I reported to my wife, "Wow. It worked!" I now recommend Blue Emu ointment myself. I have found that "it works."
Is prayer a tool? Is prayer something available for us to use, like a lawn mower or Blue Emu ointment? Would we say to someone, "Hey, try praying. If it works, great. If not, move on to something else."?
These questions are difficult to answer with a flat out No, because it just doesn't feel right to demean something as sacred and precious to so many people as prayer. But it also doesn't feel right to cheapen prayer by putting it in the same category as Blue Emu ointment--just one more thing to try, and see if it works.
I suspect that, if we're going to talk about prayer as a tool, we would do well to think of it as a tool for God's use, not ours. God's pet project is to redeem the universe, and that includes the defeat of pain and suffering, from the trivial to the substantial to the cosmic. Blue Emu ointment is one small thread in the grand tapestry of redemption. Prayer is another one, though, I think it's safe to say, a much larger and more significant one. How all these threads fit together is something we can only catch rare glimpses of from our human point of view this side of Eternity. The virtue of humility, ever an aspirational virtue, seems to call for a certain degree of reticence in our statements about just how God is accomplishing his purposes.
I shall keep praying. "While I breathe, I pray" (Andrew of Crete in the 7th century, via the magisterial translator John Mason Neale). I shall also keep an eye peeled for "God sightings"--miracles. But I'm still going to be uneasy about thinking of prayer as a tool at my disposal.