Terry,
There are literally hundreds of self promoted, unproven designs available out there. Some look to be fantastic but since they havn't actually been built, they are just that designs.
The world of small craft sailing boats is an extremely competitive world with some very difficult to handle, let alone build, highly competitive designs with state of the art rigging and sail designs. They are expensive and not for the novice.
There are some well proven, very competitive, easily built and easy to learn to sail for a youngster that are designed by well qualified, well proven designers that are quite affordable to build and rig.
But>>>>>You have to be realistic about what you expect and what you actually want to have and build and what its intended use is going to be.
I've been teaching little folks how to build small boats and to learn how to sail them and manage them when things go wrong for years. There are some boats that I strongly recommend for consideration based upon several facts.
These facts are pretty basic.
The youngster needs to know how to swim and float first and foremost. Not a distance swimmer but to respect the water and to know to some degree their own limitations and to not panic when they get dumped into the water.
The boat will capsize, and it will probably have either a dagger board or centerboard or leeboard or it will not perform well under sail.
It doesn't need ballast if designed correctly and can be shallow draft.
It can have a number of different rigs, all of which are totally suitable to learn with.
All of them will have the ability to float upright filled with water and be bailed out easily with the gunnels out of the water when floating. They will have tillers and simple rigging. None of them will be non-capsizable.
(It is part of learning to sail and handle a small boat to learn how to right it, bail it out and keep on going.) Believe me, the kids learn to respect what the boat will and won't do by pushing the envelope while under control and then to exceed that so they can learn what to do when it happens. Otherwise they are bound to get in trouble and will be exposed to a lot more danger than if they learn on a well designed, balanced and safe design with flotation.
I would recommend that you at least consider from B&B Yachts the "Spindrift 10 "
http://www.bandbyachtdesigns.com/spin.htm Many sizes and variations available from a well respected and very knowledgeable designer with many well proven designs that have lots and lots of them in the water.
It is easy to build, it looks fantastic, it is great to sail, row or use under power, either gas or electric. And it is a real blast to learn to sail in for a young person or novice adult. And it is safe! And can be extremely competitive with a little fine tuning and experience.
Also the Salt Bay Skiff from Wooden Boat Magazine. Great little learn to sail boat for kids and they can contribute to building it too. It is an easy and affordable small boat. Also a hoot to learn to sail. And a good performer. The lee board is totally practical and managable for a young person to deal with. I have 5 year old and 7 year old nephews that built a pair of them (with Dad and Uncle's help) that have spent an entire Fall learning about sailing and rowing in them. They are now in the Southern part of the USA sailing them in lakes as they Discover America and get home schooled while along the way.
A bit nicer, a little more of a challenge to the builder, and a really nice boat would be the Shellback Dinghy, again from Wooden Boat Magazine. A little more advanced but still a great boat to learn to sail in and a great rowing dingy. Not so great under power though cuz you need to have it balanced and keep the transom out of the water for good performance.
But again, lots of them built, all good performers, can be as dressy as you like or just a "plain Jane" sleeper.
All of these are light weight, easy to handle and sail. All are easily righted by even novice, lightweights once they learn what to do.
But these are quite a ways beyond the Stevenson's basic home built boats. Not to degrade the designs of Peter Stevenson in any way. But these were designed to teach novices to sail and be good handling boats with very capable and proven records. Also with good plans and documentation on being able to successfully build them. All of them can be finished off with as much brightwork as you wish to make them showpieces if you so desire. But the main thing is that all of them are well proven and successful beyond question. That in my mind equates to peace of mind, and some assurance that you are not fighting an unknown to get it to work. They are designed with the young learner and the more capable novice to learn how sailing can be when it is easy to learn.
Just my 2 cents worth but I totally respect a lot of the other suggestions as well. Just find out how many have actually been built and if the builders have been happy with them. And how successful is the designer with the design you are looking at. Lots of them look great on paper but fall somewhat short when it comes to actually building one. Lots of them offer precious little in the way of a good set of plans that you can actually build from. And lots of them are bloody expensive for no real actual performance background or record.
So have fun, but think it out from many different aspects, no such thing as the perfect boat for all uses. So get a good proven design with a good record and following. You will be much happier in the long run.