A set of variations based on a traditional German melody characteristic of the mid-18th-century keyboard style. It utilizes standard Classical figuration to elaborate on a simple folk tune.
The student must ensure rhythmic precision during rapid scale passages.
Comparable difficulty and character — good candidates for what to learn next.
21 Variations on 'Ich schlief da träumte mir' is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 21 Variations on 'Ich schlief da träumte mir' lasts about 8 minutes.
21 Variations on 'Ich schlief da träumte mir' is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include The Entertainer by Scott Joplin, 12 Variations on "Ah vous dirais-je, Maman" by Wolfgang Amadeus Mozart, Piano Sonata No. 11 in A major by Wolfgang Amadeus Mozart — see the full similar-pieces list on this page.