I know they place a lot of weight in college admissions, but do they focus on your ECs for summer programs?
You mean when you are applying to precollege summer programs, are EC’s important?
It depends on the program. Some precollege programs are not that competitive. They want to see that you are a good student, likely to get something out of the program and also not be a huge nuisance while you are with them.
There are some very competitive programs. EC’s matter there. You will want to write a compelling application and also get good letters of recommendation. Having EC’s just expands what you can write about and the types of things a teacher will be able to say about you. Applying to competitive programs is just like applying to college.