Science fairs are judged in short conversations at a display board. That format weights explanation heavily, and explanation is coachable in ways method is not.
The format constrains what can be assessed
A judge spends a few minutes per project. There is no time to examine raw data carefully, replicate a calculation or interrogate a control in depth.
So judges rely on what the student can articulate quickly: the question, why the design answers it, what went wrong and what the result actually shows.
Rubrics reflect this honestly, allocating substantial weight to communication. The scoring is not a distortion of the format; it is an accurate description of what the format can observe.
Coaching moves the coachable part
Students who rehearse the explanation with an adult improve at it quickly. Students who have no one to rehearse with present the same work less legibly.
Because that gap is invisible at the board, it reads as a difference in scientific ability rather than as a difference in access to a practiced adult.
Project topics show the same pattern. Access to a parent's workplace, a university lab or specialized equipment shapes what is possible before any judging occurs.
Confident wrongness scores well in short conversations
A student who states uncertainty accurately can appear less prepared than one who overstates a conclusion, if the judge has no time to check.
Since girls are more likely to hedge and qualify in exactly the way good scientific practice requires, the format can penalize the more careful habit.
Judges trained to ask directly about limitations neutralize much of this, because the question rewards the student who has already thought about them.
Negative results are structurally disadvantaged
A project whose hypothesis was not supported is often a better piece of science than one that confirmed something obvious, and it is harder to display.
Students learn quickly which kind of project wins, and they choose accordingly, which shapes the science being done at a formative stage.
What a fair can do differently
Fairs that require a written logbook alongside the board shift weight back toward process, because a logbook records decisions made before the outcome was known.
Fairs that offer a short presentation workshop to all entrants remove the advantage held by students who had that coaching at home.
Neither change makes judging objective. Both narrow the gap between what the fair intends to measure and what its format actually rewards.