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I don't know what clef an Eb bari sax reads, so I can't really answer the question the way you asked it.

You're trying to produce a part that allows them to play an Eb tuba using BBb fingerings, right? Personally I think it would mess up their ear worse by doing this, than if you gave them Eb parts and just wrote in the Eb fingerings for them.

But if you are determined to proceed, try this:
Write it down a perfect 4th from where you want it to sound, to have the BBb fingerings produce the right note on an Eb tuba. Change the key signature to a key a 4th down from the original key, too, so that the sharps and flats work right.

I think I got this straight, doing it with imaginary instruments in my head. If I'm backwards, somebody thinking more clearly today speak up!
MA

If they "barely know BBb", what's the problem with teaching them Eb fingerings? It's the guy who has the BBb fingerings permanently engraved in his head who has trouble.

I vote to teach them correct Eb fingerings for bass clef concert pitch.
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Joe Baker, who knows that's easy for ME to say...


EDIT: BTW, since Eb Treble Clef fingerings look the same as BBb fingerings (plus or minus 3 flats or sharps), you'd also be teaching them to read Eb TC -- they'll be ready to step into a British Brass Band as Eefers!

Bari sax parts don't transpose the tuba part. Notes stay in the same position; they just change the clef, and the key signature changes to the key up a major 6th from the original (for example, Bb [2 flats] becomes G [1 sharp]). Some accidentals need to be altered, but I'm not going to make a list.

Mary Ann has it right; transpose the part down a 4th and lose a flat (or gain a sharp).

How hard are these parts?

I'd be tempted to transpose to EEb treble clef like Brass Band music and just write in fingerings. That way, when they move to BBb, they won't be thrown off by seeing the same clef with untransposed fingerings.

There are some advantages, too. EEb's are shorter, and therefore lighter, and easier to manage for kids!

Just do it the right way and let the kids read EEb as it is. The fingering sequence is identical for both EEb, BBb, CC, and F, they just start said sequence on their name, so give the kids some credit and don't subject them to some funky made-up arrangement.JMHO

I vote for 'play it as it is'.... and learn the Eb fingerings. It won't take kids long to catch on.