I realize that there is only one weekend of the season remaining, but it is for juniors and so perhaps this information is still relevant if you have still have time to act on it. Calls (and especially mouth calls) have improved dramatically in the past thirty years. With the right calls, it is much easier for a beginner to make realistic turkey sounds. That said, there are an amazing number of really poor calls on the market-I would bet that I have thrown away five mouths calls for every one that I have tried that I like. I have also tossed a fair number of slates.
With a youngster, I would begin with a box call. A push-pin is very easy, but does not have the volume to reach out and so is unsuitable under most applications. The best box call is the old Lynch's "World Champion". It reproduces great hen and jake yelps, and produces a very respectable gobble when equipped with good rubber bands. The mahogany model is cheaper than the walnut, and sounds better too.
I rely on a very high-pitched slate call to shock gobbles out of shy or long distance birds that will not respoond to anything else. I prefer an aluminum face ("alumaslate" or equivalent). With slates, it is very important to match the call with the correct "peg", and even the manufacturers do a poor job of this. With aluminum, a soft, thick peg works best. Also, it is critical to keep the call surface rough using a piece of Scotch Brite scrub pad after nearly every call. This combination will produce fantastic cutts and yelps once you learn how to position the peg and call in your hands so that they "jump" across one another.
This slate/peg combination will not work well for soft, close-in calling. For this, he will ultimately wish to use a mouth call in order to minimize motion. This is also where a push-pin call might be a good idea. The box remains a good choice, as long as he doesn't attempt to use it while in view of approaching birds. I buy Woodhaven mouth calls--they are durable and produce the sounds they should. An easy one to use is the red wasp or the yellow jacket. They are good for about thirty hours of use if not allowed to overheat on the dashboard, etc.
Good luck!