More. . .
In addition to dr. Kaplan's answer, understand that many PDD kids are unusual socially.
They may be awkward, repetitive, often unable to understand "w..." questions such as where are you, when did you...?, who was that? Time questions are also difficult for them such as "how old are you?" PDD kids use jargon, or trivial phrases verbatim (echolalia). Pdd kids repeat tv commercials, movie lines.