I'm not a child psychologist. Nor do I play one on TV. I have not done any studies on this subject. Nor do I plan to. But I think I can safely say with confidence that by age six, the development of a child's short-term memory greatly lags that of their long term memory development.
My wife witnessed this today when she dropped our older daughter off at day camp. It seems there was an immediate issue in that Natalie, for one reason or another, was about to be kicked out of Friday's talent show by her two best friends (they planned on singing selections from High School Musical, of course). The friends were disgruntled because she told a small fib, and they decided to get back at her in a way that only six-year-old girls can do...by kicking her out of the talent show (by the way, we have not confirmed if this talent show is something actually planned by the camp, or something formulated in the minds of three six year-olds much like their previous plans to form a nationwide charity selling seashells, to fly into space together on a fuzzy carpet dressed as princesses, or to take over the government of this country and replace it with a well-trained team of puppies). At some point during the renouncing of their friendship with our daughter, my wife had to break in, sit the three of them down, and lecture them on the consequences of lying, on proper behavior amongst friends, and on how to pick on other kids without getting caught by an authority figure.
Yet by the time camp was over, the girls were literally begging to come home with my daughter and play at our house. So much for ostracizing. Thus an example of short-term memory underdevelopment. Sure, you might say it was actually an example of small children not holding a grudge. But no. I don't think so.
There are a multitude of other examples I can provide. Most have to do with performing cleanup of their playthings. Sure, when they pull out the giant box of building blocks they hear us and respond affirmatively when we say, "make sure to clean those up when you're done!" But before too long they've been distracted by the ice cream truck, and have forgotten their half-finished castle even exists.
Or, there's that moment during the bedtime ritual where they rush to the bathroom to brush their teeth, pee, and all that other stuff. As one makes her way to her bedroom we ask, "did you brush your teeth?" Usually the answer is no, because she was distracted by a shiny strand of dental floss hanging from the towel rack.
Compare this to a child's long term memory development, and there are obvious differences. About two months ago we drove by a mattress store and noticed it had burned to the ground. Virtually every day now, Jessica asks us, "Wemembuh that mattress store we saw yestuday? Why did it burn?" Obviously, it's been a life-changing event for her.
Jessica will also say on a regular basis, "wemembuh when Uncle Hillel took me in the pool yesterday? I had fun!" That was three YEARS ago.
Sometimes we play this short term memory loss to our advantage. If one asks, "daddy can you play blocks with us?" while I'm ensconced in, I dunno...blogging perhaps, I can say, "yup! Be there in two minutes". And within 30 seconds they've already moved on to crayons, forgetting that blocks exist." Of course, a week later I will hear, "daddy, you never played blocks with us yesterday," thus proving that long term memory will always take over and bite us in the rear.
Which reminds me...I promised Natalie I'd buy a goldfish for her. Hmm, that was a week ago. I'm thinking she'll mention it within the next few hours.