Does computer count as "materials for school" ?

Simple answer: yes.  

Technically the condition is that the computer must be "required".  

The IRS says:  "Whether an expenditure for a computer qualifies for the credit depends on the facts. An expenditure for a computer would qualify for the credit if the computer is needed as a condition of enrollment or attendance at the educational institution".  https://www.irs.gov/newsroom/american-opportunity-tax-credit-questions-and-answers

Apparently, the tax court has ruled on this. 

https://www.currentfederaltaxdevelopments.com/blog/2016/8/25/purchase-of-computer-from-local-retaile...

The Tax Court concluded that the cost of a computer is not eligible for the AOTC unless the school requires the student to have one.

Some have translated this to:  The IRS has indicated a computer does qualify if it is needed for attendance at the educational institution. Generally, in this day and age, a computer is necessary ("required").

Be assured: "everybody is doing it".