Dixon Beginners 308
The Dixon Beginners 308 is a jumbo pencil with a 10 mm diameter. Advertising says this pencil is "Grade matched for Kindergarten through grade 2. Large diameter fits little fingers. Extra large black graphite core for effortless writing." I believe the Beginners 308 and the blue painted Dixon Laddie 304 which says "grade matched" for grades 1 through 3 are older versions of the Primary Printer pencil seen below.
Dixon Primary Printer #1 309
The Primary Printer #1 - 309 is a red jumbo pencil with a 10 mm diameter (or 13/32 inch if you're not into metric). Dixon says that the large diameter and soft lead is "ideal for the beginner's first pencil." These pencils are still quite easy to find, however they are no longer made in North America.
Dixon Primary Printer #2 313
The Primary Printer #2 - 313 is a blue jumbo pencil with an 8 mm diameter. The Primary Printer was also made in a #3 - 314 version.
Dixon Special Black 312
This pencil is similar to the Primary Printer shown above. It also has an 8 mm diameter but was intened as a drawing pencil instead of a writing pencil. It has a long history and was marketed to schools as a student drawing pencil.