Selective Mutism is generally a disorder that begins when a child begins pre-school or kindergarten, if not before. If an older child is showing signs of SM, its safe to assume that he has been expressing this disorder for years.
If this is a new behavior, then, no - I would not think that its SM.
Additionally, SM is a specific response to anxiety. Thus, SM will often manifest itself in a new or threatening environment - not at home with people that are "safe." Thus, in your son's case, I doubt this is what's going on unless he has been diagnosed with an anxiety disorder in the past.
Does he manifest this behavior when you are asking about other things or only in response to questions he doesn't want to answer?
I will wait for your reply before going on...
Thank you, XXXXX XXXXX does help.
In general I think that he probably is shy and maybe has a personality that is quieter/clingier than some kids his age. However, being a little shy and not responding to questions/missing school are two different things. My guess is that he might be starting to exhibit some symptoms of mild defiance (which is basically my fancy way of saying that he's being stubborn - sorry!)
However, just because I don't think that this is Selective Mutism doesn't mean that his defiance isn't being caused by something deeper. Many times when kids display overt behavioral symptoms like not talking it's because they are experiencing depression or bullying and their response is simply to clam up. Do you know what his social life is like when it comes to school?
Do you know what he's doing when he doesn't go?
Well, it may be out of character and it may not be... Truancy doesn't often begin in earnest until junior high or high school for most kids. The ages of 13-15 are extremely difficult for adolescents because they are struggling to form their identity. This is when some of those patterns start to materialize and solidify. Thus, he may have been a completely compliant child in primary school, but some of these habits are just starting to come about now.
What are the consequences when he skips school - also, how are his eating and sleeping habits?
Additionally, when kids are around age 13 the emphasis changes from being on the parents to being on their friends. While parents exert the most influence in a child's life up until about age 12, it begins to shift, so a teenager's friend group is extremely significant during this period. If his friends are also skipping school or using drugs, for instance, chances are that he will follow along without some stringent guidelines to avoid this type of behavior. Do you know his friends and what their behaviors are?
Okay - so his behavior seems specifically aimed at not going to school - and his friend group seems alright. Also, he is very affected by your relationship with him and not as much by the taking away of privileges.
So, I think that Selective Mutism and Oppositional Defiant Disorder can be ruled out at this point - thank you for answering my questions.
My best guess would be that there is some stimulus at school that he is avoiding. I would have him evaluated for a learning disorder and/or depression.