Yeah, whatever, darlin. Just play that thang.

Personally I'd say the basic thing you want to be comfortable with is DUDUDUDU in whatever rhythm, and whether you are staying on the same string or moving over to another. As part of this, being able to put the emphasis on the 1st and 4th beats in a jig whether its a down or upstroke is essential. Sometimes you might want to play multiple downstrokes but it is a special effect, not something you want to be doing all the time. Places where you might use it are the first two notes in John Riley's Polka, DUH DUH da da da da daduh da duh, or if you find yourself having to play the simulated machine-gun riff in "Copperhead Road". (No doubt a song you teach in school)

I agree with Mooman that DUD DUD makes sense on a tune like Kid on the Mountain, with short emphatic phrases.

I can't think of an occasion where I would ever play multiple upstrokes, but there's a lot of things I can't think of.

W-O