During the Zoom screenings, we had the students show us their teeth and lips. They did some basic dexterity finger exercises. We had them pitch match singing things back to us. Prior to their screenings, us directors looked at their grades and classes. We also got input from their general music teachers. We did a google form students/families had to fill out before signing up for a screening time on sign-up genius that provided us a bunch of personal info that included questions like are you in piano lessons, do you play any other instruments, are you in sports, do you have any siblings or parents who play(ed) instruments. During the screenings we asked them personality questions like are they an introvert or extrovert, what are their friends like, etc. We also had parents tell us the height of their student and measure their hands. Students who didn't have a ruler or fabric measuring tape used a Coke can in their hands for us to judge hand size.
We prioritized students with piano experience for percussion and G/T kids for Double Reeds and Horn (though we still distributed these groups of kids onto other instruments as well). Before screenings, students also had to watch a video of the US Army Field Band before they were allowed to indicate their top 3 choices of instrument on the google form. (We embedded this all on the google form). For the top 3 instruments they had interest in, we then demonstrated those instruments via the Zoom screening as well and occasionally suggested another instrument that we thought would be a good fit or we needed instrumentation wise.
After interviewing each student we told them our next steps which were to screen everyone and look at everyone's top 3 choices as well as our notes we made during the screening about the students before deciding what everyone would play so that we could achieve a balanced instrumentation. As mentioned above, we did this over 2-3 weeks, but at the end of every few days of screening we'd select what instruments the students we had recently screened would play so that we could start to build a balanced 6th grade band. We did this every few days of screenings until the end - this allowed us to see what instruments we may want to push more, etc. We would slowly announce to students who had already screened with us what instrument they had been selected for and we emailed them a customized certificate celebrating this event and also sent them a pre-made blurb they could post on their social medias. Doing it this way made others excited about making sure they were signed-up to screen.
While we 100% would rather screen our kids in person, this worked out incredibly well and believe it or not, I feel that our placements ended were just as good as in-person screenings. I think we ended up with 2-3 students who moved to a different instrument due to it not working out - and that is about the same amount we'd have even if we screen the students in-person.