Mozart's K.Anh.138 is a charming but minor work, likely an early or student composition, presenting a simple theme with graceful variations. It exemplifies the clear melodic and harmonic style typical of the Classical era.
Focus on clean articulation and the precise execution of melodic embellishments.
Andante variatio (K.Anh.138) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Andante variatio (K.Anh.138) lasts about 5 minutes.
Andante variatio (K.Anh.138) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.