Both D1 and D2 have a lot of rules regarding progress toward a degree, so the following is just a rough summary, and there are lots of wrinkles-- both exceptions and "gotchas".
The NCAA doesn't think in terms of sophomore, junior, senior, etc. Instead, the rules speak of 1st year, 2nd year, etc.
In the scenario you've outlined, the player would be entering the second 4 year school at the beginning of his 4th year. D1 rules require him to have completed 60% of the requirements for his declared major at the new D1 school. This is very difficult to do if the player has spent years 2 and 3 at a JC. Most JCs don't offer courses that an ordinary student would take during his 3rd year at the 4 year school. It is truly difficult if the player has been averaging less than 15 hours per term, unless he takes summer courses. And he can't have more than 25% of his credits from summer terms.
In D2, he needs to be averaging 12 hours per term or have 24 hours during the preceeding 2 semesters (or 36 during the preceeding 3 quarters), but during and after the third year, only courses which satisfy the player's specific major count. Again, he'll need careful planning to have the right mix of courses. Summer course can help, but the 25% rule applies.
Requirements for a degree vary from school to school and among different majors, so the exact number and type of credits won't be known until he selects the second 4 year school.
