1) Just because the concept of eye gaze is simple, reading eye gaze is not necessarily easy. We need practice and experience to become competent partners. Not all kids use the same techniques, in part because the end goal for each child may not look the same (see #2).
2) Eye gaze response procedures should keep in mind technologies to be used in the child's future. If a child will be using a dwell-click with head mouse or eye gaze software, for example, then it is important that they learn to hold their gaze to a choice for a specific length of time. Children who will not be advancing to a head mouse or eye gaze may find it beneficial to confirm their choices with eye contact to the communication partner, especially if they are socially motivated.
3) Similarly, if head mouse use is in the child's future, helping them learn to turn their head along with their eyes will support that technology. This can roughly be considered "nose pointing," although the child is merely directing the nose toward the choice, rather than touching it with the nose. If head mousing is not in the child's future or if you plan to go with eye gaze not head mouse, it's fine to hold the head still and cast long sideways glances with the eyes.
4) Motor ability must be considered. The length of dwell to a choice should be reasonable...five seconds (a standard dwell time expectation in too many IEP goals, sad to say) is WAY (WAY!!!) too long for most children, both in terms of head stability and attention span. Try it...five seconds is an ETERNITY and it slows conversation down to a pathetic pace. At our house, .90 seconds is a good dwell time and doesn't interfere with the flow of communication.
5) Positioning yourself as a receiver is very important. You must be able to see the child's eyes clearly. However, some children fixate on the face of the reader, so you need to be flexible. Head-on (180*) will work for students who do not fixate on faces, but for children who are hyper-fixated on faces, an angle just over 90* may be more appropriate. You learn from the child what they need as far as positioning in relation to the partner.
6) Children with hyper-fixation to faces may benefit from loose symbols held side-by-side in front of the reader's face, then slowly moved apart. The child's eyes will (hopefully!) follow the intended choice as they move.
7) Boards intended for finger-pointing tend to have symbols spaced too closely for all but the most skillful eye gaze readers (and users). Loose symbols allow you to distance the choices at optimal points from the user. These can be held in the hands or affixed to velcro-sensitive boards (I personally like 3"-wide strips of indoor/outdoor carpet mounted to mat board, 15-18" long. Post-It makes poster board that can be cut into strips that holds symbols temporarily as well).
8) Not all days are necessarily the same. Some "off" days may require few choices spaced at farther distances, while other "on" days may allow a child to handle many choices placed closer together.
9) Along these lines of "off" and "on" days, if the child suffers neurological swings, it is imperative to tailor our expectations to the child's ability at the time. This may sound basic, but it is a point often overlooked in our hurry to take data.
10) Some children do very well with fixed frames. These are nice because they free the partner's hands and can often hold many choices. There are directions for some wonderful PVC frames online. There are also commercial e-Tran frames of Plexiglass (Cogain and others). Again, you must keep in mind the child's preferences and tendencies to fixate...
11) The goal of eye gaze communication is COMMUNICATION! It is NOT testing! Kids pick up on the fact that they are being heard or being tested, so make sure you honor what they tell you!!! This is probably the single most important point in all the discussion of eye gaze. For some reason, we tend to doubt eye gaze responses. This is because of our OWN insecurity in reading the answer correctly. If we honor a child's response, they learn to trust us as communication partners. If they indicated what they intended, we validate their answer. If they answered in error, we STILL validate their answer and demonstrate that we honor what they say. The children learn they must change their strategy to communicate the accurate answer and that they must find ways to negotiate to get what they had meant to tell us.
12) When you are unclear of a child's answer, DON'T repeat the same question. Ask it a different way. Try asking it in a way that would require they show a different answer ("Do you need more time?" becomes "Are you all done then?"). Show respect by letting the child know that you are the one having difficulty understanding; it is not the child's fault.
13) Try to keep the same placement of symbols offered for choices. This allows the child to develop motor automaticity. You may start to see eyes heading to a location before a symbol is even offered; this definitely suggests the child has achieved motor automaticity.
14) Not all children need to demonstrate "scanning of all the options" before making a selection. Motor automaticity may come to play, as well as peripheral vision skills. This does not mean kids aren't expected to know what all the choices are, but it does mean that "scanning" them may not look quite like we expect. An example is this: A teacher offered my child yes/something different/no in the same order each time (hurray! Way to build motor automaticity!) but would not accept the answer until she had gazed at each choice first. This is both unnecessary, slows communication, and discounts motor automaticity).
15) As soon as possible, eye gazers need to have introduced an option to indicate that what they want to say is not among the choices. This can be most anything ("something else," "not here," "different idea," whatever works for you and the child), but it is not fair to force a child into choosing only between choices they don't really want. Otherwise, the only option we give them is to NOT choose...and then we've set them up to be labeled as "non-communicative."
There are usual communication strategies that we can't forget: motivating topics, making the child responsible for sharing information that they alone would know (highly motivating!), respecting the answer, GENUINE conversation...
I hope this helps. Again, it's just what I've learned from walking in the trenches.