It has been done in Germany during WWII with military gliders. It was called "Hubschlepp". It was tested with a DFS 230 transport glider and a Junkers Ju 87 B-1 as a towplane. The system was very stable, only one of the two pilots had to steer his plane, the other just followed. Climb rate was roughly double that of the normal tow: 5–7 m/s against 2–3 m/s. Service ceiling, autonomy and maximum speed increased also.

https://de.wikipedia.org/wiki/Flugze...epp#Hubschlepp (in German)
See also: Ernst Peter: Der Flugzeugschlepp von den Anfängen bis heute. Motorbuch Verlag Stuttgart, 1981.