Not sure if this will help, but I *am* sure that it doesn’t really explain anything… I just wanted to empathize and show that hopefully it is a phase.
Even though I am an OLD lady now, I remember vividly going through this stage at about 12 to 14 years. I would lie about anything, even exceptionally insignificant things, even things that I knew I would not benefit from, things that were not just to get or keep me out of trouble, not just things that would make me look good (and my brother bad) but also things of no consequence. Once, I remember an adult (not sure if it was a teacher or older relative) asking me what color my eyes were. Just so you know, they are green, but I looked right at this person and told them, “My eyes are brown.” Now, they could clearly see that my eyes were/are not brown. It’s possible they looked blueish or grayish or a combo, but they surely were/are not brown. This adult looked a little shocked and gave me an out,”Oh, is that right? Well, they look kind of greenish in this light, not brown.” I could have easily said, “Oh, yeah, I was just kidding you.” But I stuck with that lie for all I was worth and to this day I don’t know why. Now that I am a mom, I sense that maybe I was needing some attention that particular day. I know that I was neglected in many ways by both parents (they seemed to find children a bother and discipline a bore). Not that this is a reflection on parents of kids who tend to lie. As you can see below, I’m having my own issues with this…
Anyway, I still remember that interaction for some reason and I think it is so that I can better help my own kids with their lying tendencies. I suffered due to that phase and not having my parents trust me and I hope to help my kiddos never repeat that history.
I agree with another poster who suggested doing the exact opposite of what your son has come to expect. Maybe if you give him no attention when he lies, barely even bothering to correct with more than “the look” (we all have one), and then showering him with praise and attention when he is responsible and makes those good choices, maybe he will respond well.
Another idea I have used with my dd-9-in-6-days is to reinact the whole situation with some suggestions of better choices. We play act the whole thing out and I ask them to change what they say to better reflect the right behavior. Even though I am usually furious at this point, I try to make this a very lighthearted exercise. That levity helps us all.
Another option I’ve used lately is this: With your blanket story, you could just offer, “Would you rather change your statement to, ‘yes, I took brother’s blanket, yes, we wrestled for it, and yes, I’m sorry he got hurt’?” If he says yes, he wants to retract his first excuse and choose the second one, let him. If he says he doesn’t like your version, ask him if there is another (third) version he would like to give. If the truth comes out, I offer praise for that behavior and minimize the punishment for lying. I make sure she sees I am thrilled with her telling the truth, with taking responsibility, for being very “grown up” about the whole situation. When I am on the phone with my mom, I make sure to tell her all about what happened and be certain to point out the bad things that *could* have happened, like she would have missed out on such-and-such activity or adventure, but she didn’t! 🙂
And then I have to exercise just enormous amounts of forgiveness and mercy to let it go. To praise her for choosing the right path and praying together very quickly to have continued good choices the rest of the school day, or the rest of the week, whatever.
Whatever you go with, I just pray you get thorough this season quickly and with the least amount of stress for all of you! 🙂