Here are some situations in which your teen might benefit from being signed up for an online high school program.
They find attending high school in person hard because of their social anxiety disorder
If your teen has social anxiety, then going to high school in person is probably hard for them. They may, for example, spend their school days fraught with worry about having to sit beside and make conversation with people at lunch in the cafeteria and might find things like science classes, where they need to pair up with a peer to do lab experiments, very stressful. These constant distractions and the exhaustion they cause your teen to feel may make it impossible for them to prioritize their schoolwork and get the grades they'd like to, even if they're intelligent and want to be studious.
In this situation, finishing high school through an online program could be the answer. This would allow them to attend their classes without having to go through the social niceties that they find so difficult and distracting. However, if there are days when they're feeling lonely and don't feel that anxious, they can always utilize the online high school's forums and interact with other students there. They will also be able to engage with their high school teachers regularly through the online program's website and via email.
Their immunity is poor and they're unwell all the time
If your teen's immune system is weak and they seem to catch and be debilitated by a new virus every other week, then it might be time to pull them out of their current high school and sign them up for its online equivalent. The reason for this is as follows: if your teen spends half the school year dealing with the congestion, tiredness, aches, and nausea that so many viruses cause, then they simply won't be able to study well, write high-quality essays or do well in tests.
Allowing them to do their schoolwork from home, where you have a lot more control over how sanitary their environment is, should cut down on the number of contagious illnesses they catch and have to take time off school to recover from. This, in turn, should give them a better chance of being able to deliver the quality of schoolwork that will get them excellent grades and allow them to apply to the best colleges at the end of their high school program.