I don't think this cartoon is a very apt metaphor for education, and in some ways it's a little offensive.
Students are not like fish versus, say, monkeys in that they are entirely different species, some of whom can climb trees and some of whom can never do so by virtue of their genetic makeup. We start in education from the premise that all students have equal potential and equal ability to learn. All students are smart (and if you've ever been in a kindergarten or first-grade classroom you will know that is true). What students don't have is equal opportunities, equal living situations, or equal support.
Look, there's nothing wrong with standardized testing per se. It's existed since I was in elementary school, and I'm in my 60s. What concerns us is when so much effort is put into "teaching to the test," and when it is used to reward or punish schools. But testing can be a useful tool for helping to identify various children's needs ... be they kids who are failing the tests and need more help or kids who are acing them and need more challenging material.
Tests aren't bad in themselves. It's the uses to which they're put. And no, students aren't like Einstein's differently abled animals. All students have the "ability" to learn, and our aspiration should be that they all do so to the best of their ability. They just need different kinds of help, each according to her needs.