I don't think it would be necessary for just learning in shallow water, especially if you are in an area where you have easy access to the water. I don't know much about water loving breeds, but chances are at 4 months old he will just want to splash and play rather than swim. I can't picture a 4 month old pup being coordinated enough to swim (again this is coming from a non water loving breed lover...LOL).

But for the boat I think it is a good idea. Emily has a life jacket that I got for her when we had a boat. If we ever get a boat again in the future then Clipse will get one too.