Exactly what it says on the tin. This is clearly a German 10 mark note of some kind, but I can't find pictures online of any notes like it.
The reverse is completely blank, with some bleed-through from the "DRINGEND" stamp. The white balance on my camera is rather off, and the note is actually far more yellowish than the photo implies.
So, the question is twofold:
The design is that of the "sailing ship" 10 Deutsche Mark note, a banknote first issued in 1960. The front features a 16th century painting by Lucas Cranach the Elder. On a real version of the note, the reverse would have depicted a barque of the same type like the German navy sailing ship Gorch Fock, officially meant to represent German openness to the world.
These notes were withdrawn from circulation in 1990.
A sample of the real 10 mark note found on Pinterest via Google
However, in your case the RECHENGELD stamp denotes that it is only play money, used for educational purposes according to @Loong in the comments. Which also explains why the reverse is blank.
This is an addition to Semaphore's answer:
This is the 10 D-Mark note of the third edition of the Deutsche Mark, the Gemäldeserie BBk I (1961) (painting series).
It was designed by the Swiss designer and artist Hermann Eidenbenz who was living in Hamburg, Germany.
It was printed between 1961 and 1990. There are five printing runs which are mentioned under the signature in the lower left corner:
1: 2. Januar 1960 (January 2nd, 1960)
2: 2. Januar 1970 (January 2nd, 1970)
3: 1. Juni 1977 (June 1st, 1977)
4: 2. Januar 1980 (January 2nd, 1980)
5: Change of copyright, no change of date
The red "Rechengeld" stamp means that it is money for children to learn using cash. The blue stamp "Dringend" only means "Urgent", I do not know what purpose it has.
To all anglophones: It is Deutsche Mark, D-Mark or even shorter simply Mark, not Deutschemark or Deutschmark or — simply stop it, ok?
Yeah, I know how it is called in English, but it was always grating to German ears.
It is evidently a play money banknote that is modeled after the BBk I series in print from 1960–1970 (while the whole design was indeed issued until 1990).
Reasons:
The serial number seems not only to be coloured wrongly, but also has characters all of the same height. This was changed mid-series in 1975: the red numbers would then start with characters which were 0.6 mm larger then the rest.
(—Source: Deutsche Bundesbank: "Kursfähige Banknoten", January 1986. PDF)
The signatures on display in the question are those of Karl Blessing and Heinrich Troeger (the last using his preferred first name "Doctor", then president and vice-president of the Bundesbank:
Real banknotes of this kind would have circulated only from 1963 onwards.
Note that I write the bill is modeled after that series. As most wouldn't notice the subtle differences anyway, this actual play-bill in question might also have been printed later.
— Bundesbank 1986, showing the latest signatures, click for large
Which narrows this down to the model used after comparison of possible signatures
A later model of this exact Rechengeld shows the signatures of Klasen/Emminger and a date of 1970, making this based on the model from between 1975–1977:
— Src: Spielgeld DM; although that one has the proper reverse printed as well.
Should anyone be into collecting this stuff:
— Günter Aschoff: "Deutsches Kinderspielgeld: ein numismatisches Randgebiet", Ed. M&S, 2009.
