The Curious Researcher, by Dr. Bruce Ballenger, is a college-level textbook that walks students through the process of writing a research paper. It's an excellent text and also useful with older middle schoolers or high schoolers (although some of the illustrations are a bit grown-up for the younger crowd and may need to be replaced).
However, I found that my younger students had a hard time keeping the big picture in mind, so I made this checklist. The checklist summarizes the process of planning, researching, and writing the paper, and corresponds to Ballenger's text (7th edition). One version is annotated with exercise/page numbers for reference. The teachers' version includes notes indicating convenient points of the process for further exploration of related skills (such as effective searching).
Although I highly recommend the book, the checklist can stand alone.