How do I get photos for slide show in a particular order?

I have 134 photos I imported into iPhoto, in a particular order. When I imported them, the slide show wasn't totally in the same order as they were in my file. So I thought I would number them all, thinking, "Ah, now iPhoto will surely keep them in the same order." The order was sooo random… they were all out of order so badly, I have no idea what to do now. Can anyone tell me how to keep the slides in order? Is it going by the date I edited them? I want it to pick them up by the order they are in, in the folder they're in. I hope someone can help me. Many thanks!!!