Here are the requirements:
American opportunity credit: Credit of up to $2500 for qualified education expenses
needed for a course of study, paid for an academic period starting in 2018 or the first 3 months of 2019

Here are the qualifications for the American Opportunity credit:
1. It is available only for the first 4 years of post secondary education and cannot be claimed more than 4 tax years.
2. Student must be pursuing an undergraduate degree or other recognized education credential.
3. Student must be enrolled at least half time for at least one academic period beginning during the year.
4. No felony drug conviction on student's record.
5. Credit is reduced if modified AGI is between $80,000 and $90,000 ($160,000 and $180,000 if MFJ)
6. You cannot be claimed as a dependent by someone else.

Do you meet these requirements?

My son is in his second year of school and I meet the AGI requirement and all the others. I paid almost $16000 towards his schooling in 2018. Not sure why TurboTax does not give me the credit this year.

Go back through the questions in the AOC interview and make sure you answered them correctly. Did his school correctly report tuition and fees paid in box 1 of the 1098-T? Some schools are apparently still reporting amounts billed in box 2 which is no longer allowed by the IRS.

Yes, his school reported the amount in box 1

Thanks for your help. I went back and I had missed some questions because TurboTax didn't prompt me to automatically answer them. Thanks so much,