rather than an outright lie?
Ds1 is 14yo. When he was 10/11/12 we had a big problem with lying - he would lie almost as an automatic reaction, when there wasn't any need, over the simplest of things.
After some serious sanctions I thought we'd made progress and I haven't caught him out for a couple of years...must maybe he's just got better at it 
He is notoriously bad at remembering to hand things in at school. This week he's had two letters to go back. One about a French trip he wants to go on and one about English tutoring he's been offered but is less happy about. I've reminded him every morning but he still had them both yesterday eve. I told him this morning that the French trip is up to him but he absolutely must hand the English one in today, or else! It's been offered because he hasn't made the required progress this year and is not optional as far as I'm concerned.
When he got home tonight his first words were "I've handed in both my letters". I even congratulated him!
Then he went off for the weekend with Scouts and I picked his blazer off the floor only to find the English letter in his pocket. To say I'm furious/sad/disappointed is an understatement. The school want my permission for the tutoring and won't schedule the sessions until they have it.
So, he's for it when he gets home on Sunday. What's his excuse going to be and do I listen when he says he "forgot" he hadn't done it?