Rhythm - you can count on it.

My life has given me an interesting opportunity to interact with a LOT of band kids from all over the place and in a variety of ways. As a marching arranger, I often get to visit with the programs for which I write. As a drum corps instructor, our audition process brings us many more players that we have spots for. As a composer, I get the chance to Zoom into a band room to talk with students. And over this past year, editing virtual ensembles, I've been really into the weeds with individuals' performances. 
I really can't stress enough how important it is for bands kids - from the very beginning - to know how to count. 

Imagine, if you will, your first foray into triangles in geometry class and your math teacher teaching you all about right triangles, makes you memorize all the common sizes (3-4-5, 6-8-10, 5-12-13) - but never teaches you the Pythagorean theorem to be able to figure it out on your own.
Imagine being in middle school English class - I think we can all remember the stress and agony over all those spelling words. But after learning all those big and fanciful words, you don't know the definitions of them to use them in a sentence. 

This is band without rhythm.

I've heard a LOT of band students, even at the middle school level, who have a pretty good sound (even if just for their age). But past that beautiful sound, sight-reading is a mystery due to their not being able to decode the rhythms on the page.

One of my greatest successes as a teacher - I worked for a year in a challenging school. My band was very small: 14 students in the class. I had 5 winds, 2 mallet players, and 7 drummers. They ranged from beginner to "could be a music major" in ability. Trying to play ensemble literature on day 1 was folly. 
I spent quite a bit of time through the year teaching them music theory. Not even theory - just "Literacy." On the A/B Schedule (I saw them alternating days), we would sometimes have a 3-day band week where we'd spend 2 days on "theory." They learned how to read the notes on both Treble and Bass clefs, including ledger lines. They learned enharmonic spellings. They learned how to build Major and minor scales. And they learned to COUNT. Everything down to 16th notes. All the dots in the world. Sometimes a double-dot, just for fun (since they knew exactly what a dot meant, double and triple dots didn't faze them). We did meters with 2, 4, 8, and 16 on the bottom. Symmetric and asymmetric. By the end of the school year, kids who couldn't play a Bb scale knew how to sight-read at a good Grade 3 level. 
Because of the efforts that went into teaching Literacy - rather than shouting rhythms at them by rote - the students could put together a respectable concert program over a matter of a few weeks, rather than few months.

Teach your kids to read. It makes all the difference in the world.