Why do you need 打算?
You need a "going to" so you need a word pointing to the future; either 会 (will) or 打算 (plan)
打算 means "to plan to (do sth.)"
选择 is often abbreviated as 选, but this is flagged as incorrect.
Wouldn't 家 be better here?
Why is 他会选择哪家学校 wrong?
If anything there should be a 会 in there, but the 打算 is definitely not expressed in the english translation.
I think "他會選擇去哪個學校？"—using the grammatical format from another exercise in this lesson—should also be accepted given the English reference text, which includes nothing about "planning".
It does. "Which school does he plan to choose?" pretty much means, in more common English: "Which school is he going to choose?"
they're not interchangeable though! you can guess what school he will choose without knowing his plans, and conversely a plan is not a concrete statement about the future
and why 那个? the question was about 'that school'
please disregard. i was confused...
i meant to write 'not', it is not about 'that school'