Final answer:
A student permit becomes invalid when a student obtains a full driver's license as this indicates they have completed the requirements necessary to transition from a permit holder to a licensed driver.
Step-by-step explanation:
A student permit typically becomes invalid for various reasons, such as upon graduation or while awaiting to take a driving examination. However, the specific conditions listed in the question indicate that a student permit is no longer valid if the student obtains a full driver's license. This is because the student has moved beyond the learner's permit stage, having demonstrated the necessary knowledge and practical skills to earn a full license. Other options such as turning 18, completing a driving course, or getting a job do not inherently invalidate a student permit.