Another perspective, with a biochemist parent's interpretation is available from the National Alliance for Autism Research. Look under NAAR Review - Secretin and Autism for an excellent report. These links alone will direct you to many other interesting pages. The way it is applied is thought to have much to do with its effectiveness. The secretin is mixed with anhydrous PLO gel which is run through an ointment to improve the absorption.
Progress tends to happen quickly thereafter.
The expectation is for social skills and interaction with other children and adults. Self stimulating behaviors decrease. Children with poor appetites seem to take on new food interests. Verbal skills improve. Bowel movements and potty training improve.