How Much Does ACT Writing Matter in Applications?

Hello,
I am a sophomore in high school and am looking to apply to some Ivy League schools, MIT, Stanford, etc. I have a 36 ACT Composite (36E, 35M, 36R, 35S), but am concerned about my writing score (24), which seems to be below average for schools of this caliber. These are my three questions:

  1. How much emphasis do schools that require the writing portion place on it?
  2. Does this vary between different types of schools? (for example would Harvard place more emphasis on the writing test than a school like MIT)
  3. Since my main interests are in math and science, will this affect how much weight colleges put on my writing score?

What state are you from? On most college websites it says if the writing portion matters.

Arkansas