Who did you say you are?
I am the author of more than 20 books, primarily for middle grade students and teens, mostly science fiction and fantasy (including A Hidden Magic, Smart Dog, Never Trust a Dead Man, and Troll Teacher).

Presentation:  From Idea to Book
My presentations are about an hour long (depending on the school's schedule).  I give an informal and anecdotal talk of approximately 15 - 20 minutes, telling how I got started writing and showing some of the stages a manuscript goes through during the publication process, including making revisions. The rest of the session is for questions and answers, and usually covers such topics as: Where do you get your ideas? What do you mean you don't choose the illustrations? Are you rich? Do you know J.K. Rowling (or Stephen King, or...)?

Audience age, size of groups, fee
My presentations are geared toward 4th grade and up.
Groups of fewer than 100 students are the ideal size, since I use transparencies to show images; in larger groups, students would have trouble seeing the screen. 
For visits in the Rochester, NY, area, I charge $1,000 a day, with 3 sessions a day.
For locations more than 50 miles from Rochester, the charge is $1,500 (+ travel) per day, with 3 sessions per day.
I am happy to sign books (which does not count as a session).

Needs
An overhead projector and a room which can be at least slightly darkened. 

Note:  School visits are most worthwhile to the students if they are familiar with at least one of my books or short stories because then we can talk about specifics:  how I came to write that story and some of the choices involved.

Writing workshop for kids
If, instead of a lecture, you're interested in a writing workshop, that definitely needs to be with much smaller groups of children (absolutely no more than 25).  A workshop would cover such topics as descriptions that use all the senses, characters (who they are and what they want), and conflict (happy life = dull story).  Depending on how much you want covered and the age of the students and if the students will be sharing their own work, this can go from one hour to an all-day session. 

Writing workshop for teachers
In leading workshops for adults, I've found that many of my adult students are teachers who are interested in becoming writers.  If there are enough teachers in a school (or district) who are interested, I would be happy to discuss the possibility of a workshop for them after school hours or on a weekend or vacation day. 

Having an author or illustrator come to talk to your class or library can be fun, informative, and inspiring.

Bear in mind that each author is different, with different talents and different ideas of what works. Bring in two authors, and you will probably have two sets of expectations. Authors who speak at schools have a wide variety of formats from performance to lecture to workshop, are willing to speak to different size groups (some are willing to speak in an auditorium to the entire school, others--because of the nature of their talk/activity--limit their audience to one classroom at a time), and some require special equipment or set-up.

Therefore, it is important that you discuss your expectations with the author to make sure of a good fit between your needs and what the author is comfortable doing.

Knowing What to Expect... (Can You Put That in Writing?)
It is always wise to establish in writing the date and time of the school visit, how many and what kind of sessions you expect the author to give, what grade level(s) he or she will be addressing, and what size the groups will be.

Provide the author with the name of a contact person--someone who will be at the school that day. (For example, the librarian.)

Let the author know if payment for services will be given on the day of the presentations or if your school expects to mail the check afterwards.

Grade Level
The author's presentation may well be geared to a specific age. Therefore, if the author says he/she is willing to speak to grades 6 -12, don't ask him/her to read a story to the kindergarten class.

And, just as you would find it difficult to teach a group that includes both 2nd graders and 5th graders, authors find it is most beneficial if a presentation session includes children from only one grade level.

Is That Negotiable?
Some authors might be willing to speak to older or younger grades than they've indicated, if doing so will include the whole school. But others are firm. Check beforehand.

How to Get There
Even if the author is in the same city as you are, don't assume he/she knows how to find your school. Be prepared to provide a map or directions to the school, including instructions on where to park and which door to come in.

Visits from Out-of-Town Authors/Illustrators
If your author is coming from out of town, the school should assume it will be responsible for making and paying for plane or train reservations and should not expect the author to pay and then be reimbursed after the visit. Either make arrangements to pick up the author at the train/plane/bus station, or make clear that he/she should take a taxi (and be reimbursed for that).

As far as overnight stays: No matter how well you and the author may get along, he/she needs quiet "down time" and should be put up in a hotel or bed & breakfast, not in the spare bedroom of one of the teachers.

May I Have Your Autograph Please?
Most authors are glad to provide autographs, especially if they know in advance they will be doing this. While authors may be willing to sign their own books that children have brought from home and children's friendship or autograph books, please do not permit children to ask authors to sign individual bookmarks, scraps of paper, articles of clothing, or body parts. If you want a souvenir for everyone, ask the author to sign a bookmark which can be photocopied for those children who do not have books.

Speaking of Books, Are You Planning To Have Books Available for Sale?
Books make a lovely keepsake of the day. Some authors have their own supply of books that they can bring to a school visit. On the other hand, many do not. Be sure to ask. If you expect to sell books, you will have to make arrangements with a book store or book seller several weeks in advance to make sure no one is disappointed.

When Do We Eat?
If the author will be at the school over the lunch period, what provision will be made: Will the author be provided with a lunch, be expected to bring his/her own, or be pointed in the direction of the cafeteria? Sometimes schools like to plan a special lunch program with selected students or teachers. Most authors are willing to be flexible, so long as they know what to expect before they get there.

Whether the author will be at the school all day or for only two sessions, the sessions should have at least a few minutes in between to give the author a chance to catch his/her breath and to get any materials back in the proper sequence for the next group.

How Long in Advance Should the Author Be Contacted?
Some authors have their schedules filled out a couple years beforehand; others have enough leeway they can be more spontaneous. The more time you can give the author to prepare for your school visit, the better.

And Speaking of Preparing for Your School Visit...
This day will be more enjoyable and most beneficial for your students if they have been prepared for the author's coming. Have the students read, or read to them, one of the author's stories beforehand. That way students and author can talk in a meaningful way about such specifics as how the story came to be written (or illustrated) and what were some of the choices that had to be made.