Schubert's Allegretto in D major, D.346, is a delightful miniature offering a glimpse into his melodic genius. It is characterized by its flowing, song-like quality and its gentle, introspective mood.
Focus on a beautiful singing tone and sensitive use of rubato to shape the phrases.
Allegretto (D.346) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 Allegretto (D.346) lasts about 2.5 minutes.
Allegretto (D.346) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.