Sebastian took 3 years of Latin in high school. In college, he takes three courses in Spanish. By the end of college, he finds it hard to remember much Latin. Sebastian is experiencing interference.

The answer is retroactive interference.

Explanation:

Retroactive interference is a retrieval impariment in which new information interferes when remembering older information. For example, after one year with a new phone number, a person might forget his older number. This is related to the recency effect, which states that people remember the most recent information best.

The opposite is called proactive interference: older information interferes when creating new memories.