I'm doing a bit of head scratching. Can anybody recommend anything by Mozart that's suitable for somebody between Grades 3 and 4? (A very precise and articulate player, good reader for the grade, and quick learner.) Closer to 4 than 3, maybe even touching 5, but not long? The specifications I've been given by the pupil are 'Mozart, major key, quick tempo, bright and bouncy, but pretty short'.

Anybody got any suggestions?

A transcript of Eine Kleine Nachtmusik?

I know it's not quite a fit for the description, but I'd say go for the K545 Andante. It will be a challenge, but very rewarding I had a mental block on pieces longer than 1 page for quite a while but once I broke through it it wasn't a problem.

How about some movements from the Viennese sonatinas or
Theme and 1 or 2 easiest variations of Ah vous je dirais maman (twinkle).
There are also short Mozart compositions like the early compositions, menuets and the later German Dances.

3 Petits Morceaux Pour Piano. K15
Variations In A. K 454a (Selection)

I still cannot understand why I had to play first movement of K332 for Grade 4, way back in 1959 (LCM) when ABRSM set it for Grade 8 recently. I reckon its probably about Grade 6 standard, as is 1st movement of K331 and K282.
K545 second movement is probably the easiest Sonata movement by Mozart, but its at a slow tempo. However the first movement may not be impossible for a dedicated practiser of Grade 4-5. BUt none of the sonata movements meet your specification 'short'.
How about just the first minuet of the two minuets (second movement) in Sonata K282 ?

Thank you very much, folks!
I only have time to log on and off at the minute, but I'll look into all your suggestions later this evening.

I know Paradies' Toccata is supposed to be beyond the level that I'm talking about, but I have this in the back of my head too as something she'd really like, even if we only look at the first section.

Because the grade is not a measure of the piece, but of the pianist!

You really need to be a good professional concert pianist to really do full justice to most of the Mozart sonatas (and even then a good result is by no means certain)

So ... it is possible to make a reasonable attempt at K322 at Grade 4, but a performance that would earn you top marks at Grade 4 would be a failure at Grade 8.

Theres a short Mozart piece in the grade 3 ABRSM syllabus this year. It's in the Associated board exam pieces books. Its an Allegro in F if I remember correctly.