"No, prayer does not always work. Neither does science"
The slight difference being that when science doesn't work you can find out why and correct for that. With prayer it's all down to the mood the sky fairy de jour is in and praying harder or differently doesn't help.
If prayer was anything like reliable then you would be able to repeat the experience and vary the prayer in a measurable way to affect the outcome. With 1000's of years of "practice" you'd think the various religions would have prayer down pat by now instead of random hit or miss.