Is it true that Christopher is an unreliable and ineffective first person narrator in The Curious Incident of the Dog in the Night-Time?

Actually, depending on how you look at it, Christopher's
condition as having autism makes him probably one of the most truthful narrators you
could possibly imagine. He himself says that he cannot tell lies and has to tell the
truth. However, what your question is pointing towards is the way in which we tell the
truth from our own perspective. And this is the important point for this excellent
novel. Christopher does, as he says, tell the truth, but we are forced to recognise that
he is only able to tell the truth from his reality and understanding. As his autism
makes his understanding of human interactions limited, we are often in a position that
we, as readers, are able to see the real truth of what Christopher is observing, when he
is only puzzled by what is happening. You could use some of the interactions between
Christopher's father and his mother, or his father and the neighbour, Mrs. Shears to see
this. Christopher, throughout the novel, struggles to understand the complex actions and
motives of the adults that surround him, and why they have deceived him, such as his
father lying about his mother's "death."

Thus I would
question the words "unreliable" and "ineffective" in your statement. Christopher is
actually incredibly truthful, but it is his ability to understand the complex
interactions of humans that make his account partial and
limited.