Can a student with a couple of Bs and strong standardized test scores have a chance at those schools given the student has OK but not stellar ECs?
You’re talking about schools with single digit acceptance rates for students with perfect everything. Do you have a chance? Yes. In the very, very low single digit percentile.
I would disagree that students with perfect everythings have single digit acceptance rates. There was a recent thread based on the Harvard litigation where there is evidence to suggest students with perfect to near perfect test scores and gpa had an acceptance rate in the 30%+ range. In this profile page for Stanford for the 2016 admissions cycle https://admission.stanford.edu/apply/selection/profile16.html, scoring an 800 just in one component of either the reading or writing subsection yielded an admissions rate of 12% and 13%. That having been said, having perfect everythings does not come close to guaranteeing admissions at the tippy tops like Yale and Stanford. On the other hand not all accepted students have perfect gpa’s or test scores.
For OP’s purposes, what exactly does a couple of B’s really mean. Are you taking the most rigorous courses your school offers? What is your approximate class rank, top 1%, 5%, 10%? After the objectives, it will be how you represent yourself in the app through your LoR’s, EC’s and essays. Will the LoR’s give a personalized insight on why you are special with specific anecdotes to support the recommendation; will the EC’s show characteristics related to commitment, leadership, teamwork, perseverance, generosity, curiosity, etc…; will your essays also support some or all those characteristics such that given the whole package, the school believes you will make the best use of the school’s resources and that you will be a contributor to the school’s overall community?
Chances are not great. Not because of your grades or test scores, but because the lack of stellar ECs (ofc that really depends what you mean but stellar, but if you don’t find it impressive, I don’t think admission will either)