Arado 68 E biplane fighter, powered by a Junkers Jumo 210 engine and used in the trainer role. Aircraft's likely fuselage code, S7+B94, would point to Schule/FAR (Flieger-Ausbildungs-Regiment) 13 at Neubiberg, Bavaria, in late 1939. Aircraft seems to be painted 63 on all surfaces.
Note unusually large Balkenkreuz on underside of lower wing (see detail enlargement) as well as heavy staining below exhaust stacks.
Aircraft in the background is in all probability a Focke-Wulf Fw 44 Stieglitz [goldfinch] biplane trainer. It displays equally large under-wing crosses. (Fischer collection; additional information very kindly supplied by Eric Guillaume)