The meaning of a certain symbol can change depending on the culture. Here are some example's i could find related to your question (I hid the answer to see if you can guess correctly):
In Sweden, what does ✓ mean on a test?
It is commonly used to indicate an incorrect answer.
In Holland does a 'V' icon mean correct or incorrect on a test?
It is commonly used to indicate an incorrect answer. I can confirm this as I am from Holland.
Also according to Wikipedia, the O mark is used in east Asia the same way an X mark is used in Western countries.
In a lot of Western countries a ✓ mark will mean 'correct', while an X mark will mean incorrect. However, in certain situations it will not provide the correct. It is extremely hard to find one icon that is used by everyone the same way. I think it is best if you use a legend to show what a certain icon means.
So something like:
✓ = Present
Another thing you can do is only show if someone has not been present, you can maybe change the icon to something like an exclamation mark when someone has not been present.