Gyre sage, terastodon

[Taysby]

So my Friend has out {gyre sage}, and he plays {terastodon} and he evolves his elf.  He then sacs 3 of his lands to get 3 3/3's.  how many times does the sage evolve from the 3/3's?

H thinks that they all enter the battlefield at the same time, and its power was 2 when they enter so it evolves 3 times.

I think that the sage has to check its power/toughness every time a counter would be placed on it so it would only evolve once.  Who's right?

[Arbitratur]

It says "when  {Terastodon} enters the Battlefield" so first {Terastodon} enters, {gyre sage} checks and evolves to a 2/3, then the other 3 elephant tokens enter, checks with the first, evolves to a 3/4, then it checks with the other 2 which do not cause it to evolve,

So the answer is that it evolves twice.

[Kaleo42]

It says "IF their P/T is bigger" this is called an intervening if clause. That means it checks both when the trigger happens and when it resolves. It would trigger 3 times and only place 2 counters.