There are a number of factors that can determine if a JC student-athlete can be a "one and done". Sometimes such a player comes to a JC with prior course credits that they can use. If they are a bit ambitious, they can take, besides their normal course load, some on-line five week courses to gain extra credits, as well as take summer classes. Yes, many, if not most, JCs have summer courses.
A bit off subject, but remember the "Truth" only spent one year at San Jacinto JC. If memory serves me right, Walter was at St. John's first, then JC for a year, and back to us for two out of three possible years.