Final answer:
Equivalence class partitioning assumes that all elements within an equivalence class will be treated the same, which is true. This technique is used in software testing to efficiently select representative test cases.
Step-by-step explanation:
The critical assumption in equivalence class partitioning is indeed that each element within a given equivalence class is expected to be treated the same as every other element in that class. This assumption is true for the purpose of software testing, where equivalence class partitioning is a technique used to divide a set of test inputs into partitions of equivalent data from which test cases can be derived. The principle behind this technique is that testing a value from each partition is representative of testing all values within that partition, assuming they will behave the same way in terms of discovering potential defects.